diff --git a/packages/layout-engine/painters/dom/src/index.test.ts b/packages/layout-engine/painters/dom/src/index.test.ts
index 4a682ff56a..0940a45039 100644
--- a/packages/layout-engine/painters/dom/src/index.test.ts
+++ b/packages/layout-engine/painters/dom/src/index.test.ts
@@ -6539,7 +6539,7 @@ describe('Link accessibility - Focus styles', () => {
     const styleTag = document.querySelector('[data-superdoc-link-styles]');
     expect(styleTag).toBeTruthy();
     expect(styleTag?.textContent).toContain(':focus-visible');
-    expect(styleTag?.textContent).toContain('sr-only');
+    expect(styleTag?.textContent).toContain('superdoc-sr-only');
   });
 
   it('should not inject styles twice', () => {
@@ -6954,7 +6954,7 @@ describe('Link accessibility - Tooltip aria-describedby', () => {
     // Look for the description element in the mount, not document
     const descElem = mount.querySelector(`#${describedBy}`);
     expect(descElem?.textContent).toBe('Visit our homepage for more information');
-    expect(descElem?.className).toContain('sr-only');
+    expect(descElem?.className).toContain('superdoc-sr-only');
   });
 
   it('should maintain title attribute for visual tooltip', () => {
diff --git a/packages/layout-engine/painters/dom/src/renderer.ts b/packages/layout-engine/painters/dom/src/renderer.ts
index 191c35b3df..ee92278766 100644
--- a/packages/layout-engine/painters/dom/src/renderer.ts
+++ b/packages/layout-engine/painters/dom/src/renderer.ts
@@ -4047,7 +4047,7 @@ export class DomPainter {
     const descId = `link-desc-${linkId}`;
     const descElem = this.doc.createElement('span');
     descElem.id = descId;
-    descElem.className = 'sr-only'; // Screen reader only class
+    descElem.className = 'superdoc-sr-only'; // Screen reader only class
     descElem.textContent = tooltip;
 
     // Insert description element after the link
diff --git a/packages/layout-engine/painters/dom/src/styles.ts b/packages/layout-engine/painters/dom/src/styles.ts
index c711b85f18..0b936c1ff4 100644
--- a/packages/layout-engine/painters/dom/src/styles.ts
+++ b/packages/layout-engine/painters/dom/src/styles.ts
@@ -185,7 +185,7 @@ const LINK_AND_TOC_STYLES = `
 }
 
 /* Screen reader only content (WCAG SC 1.3.1) */
-.sr-only {
+.superdoc-sr-only {
   position: absolute;
   width: 1px;
   height: 1px;
diff --git a/packages/super-editor/src/assets/styles/elements/ai.css b/packages/super-editor/src/assets/styles/elements/ai.css
index 282815d057..b4cabe4eeb 100644
--- a/packages/super-editor/src/assets/styles/elements/ai.css
+++ b/packages/super-editor/src/assets/styles/elements/ai.css
@@ -1,16 +1,16 @@
 /* Custom toolbar styling */
 
 /* AI button icon styling with gradient */
-.toolbar-icon__icon--ai {
+.super-editor .toolbar-icon__icon--ai {
   position: relative;
   z-index: 1;
 }
 
-.toolbar-icon__icon--ai svg {
+.super-editor .toolbar-icon__icon--ai svg {
   fill: transparent;
 }
 
-.toolbar-icon__icon--ai::before {
+.super-editor .toolbar-icon__icon--ai::before {
   content: '';
   position: absolute;
   top: 0;
@@ -33,12 +33,12 @@
   transition: filter 0.2s ease;
 }
 
-.toolbar-icon__icon--ai:hover::before {
+.super-editor .toolbar-icon__icon--ai:hover::before {
   filter: brightness(1.3);
 }
 
 /* AI text appear animation */
-@keyframes aiTextAppear {
+@keyframes superdoc-aiTextAppear {
   from {
     opacity: 0;
     transform: translateY(5px);
@@ -49,27 +49,27 @@
   }
 }
 
-.sd-ai-text-appear {
+.super-editor .sd-ai-text-appear {
   display: inline;
   opacity: 0;
-  animation: aiTextAppear 0.7s ease-out forwards;
+  animation: superdoc-aiTextAppear 0.7s ease-out forwards;
   animation-fill-mode: both;
   will-change: opacity, transform;
   /* Ensure each mark is treated as a separate animation context */
   contain: content;
 }
 
-.sd-ai-loader {
+.super-editor .sd-ai-loader {
   display: flex;
   justify-content: flex-start;
 }
 
-.sd-ai-loader > img {
+.super-editor .sd-ai-loader > img {
   width: fit-content;
   height: 40px;
 }
 
-@keyframes ai-pulse {
+@keyframes superdoc-ai-pulse {
   0% {
     background-color: rgba(99, 102, 241, 0.1);
   }
@@ -81,6 +81,6 @@
   }
 }
 
-.sd-ai-highlight-pulse {
-  animation: ai-pulse 1.5s ease-in-out infinite;
+.super-editor .sd-ai-highlight-pulse {
+  animation: superdoc-ai-pulse 1.5s ease-in-out infinite;
 }
diff --git a/packages/super-editor/src/assets/styles/elements/page-number.css b/packages/super-editor/src/assets/styles/elements/page-number.css
index ffacbb5e1d..7ae846bd60 100644
--- a/packages/super-editor/src/assets/styles/elements/page-number.css
+++ b/packages/super-editor/src/assets/styles/elements/page-number.css
@@ -1,20 +1,20 @@
-.sd-editor-auto-page-number,
-.sd-editor-auto-total-pages {
+.super-editor .sd-editor-auto-page-number,
+.super-editor .sd-editor-auto-total-pages {
   transition: all 250ms ease;
   border-bottom: 1px solid #9a9a9a;
   cursor: not-allowed;
 }
 
-.sd-editor-auto-page-number:hover,
-.sd-editor-auto-total-pages:hover {
+.super-editor .sd-editor-auto-page-number:hover,
+.super-editor .sd-editor-auto-total-pages:hover {
   border-bottom-color: #4f4f4f;
 }
 
-.sd-editor-auto-page-number-content {
+.super-editor .sd-editor-auto-page-number-content {
   pointer-events: none;
 }
 
-.ProseMirror.view-mode {
+.super-editor .ProseMirror.view-mode {
   .sd-editor-auto-page-number,
   .sd-editor-auto-total-pages {
     border: none;
diff --git a/packages/super-editor/src/assets/styles/elements/prosemirror.css b/packages/super-editor/src/assets/styles/elements/prosemirror.css
index af738f2d72..064e21bf61 100644
--- a/packages/super-editor/src/assets/styles/elements/prosemirror.css
+++ b/packages/super-editor/src/assets/styles/elements/prosemirror.css
@@ -1,14 +1,17 @@
 /**
  * Basic ProseMirror styles.
  * https://github.com/ProseMirror/prosemirror-view/blob/master/style/prosemirror.css
+ *
+ * All selectors are scoped under .sd-editor-scoped to prevent bleeding into host apps.
+ * See: SD-1850
  */
-.ProseMirror {
+.sd-editor-scoped .ProseMirror {
   position: relative;
   /* We use "all: revert" to isolate the editor content from external stylesheets. This makes the "contenteditable" not editable on Safari devices. So we need to keep this. */
   -webkit-user-modify: read-write-plaintext-only;
 }
 
-.ProseMirror {
+.sd-editor-scoped .ProseMirror {
   word-wrap: break-word;
   white-space: pre-wrap;
   white-space: break-spaces;
@@ -18,35 +21,35 @@
   z-index: 0; /* Needed to place images behind text with lower z-index */
 }
 
-.ProseMirror pre {
+.sd-editor-scoped .ProseMirror pre {
   white-space: pre-wrap;
 }
 
-.ProseMirror ol,
-.ProseMirror ul {
+.sd-editor-scoped .ProseMirror ol,
+.sd-editor-scoped .ProseMirror ul {
   margin-block-start: 0;
   margin-block-end: 0;
   margin-inline-start: 0;
   margin-inline-end: 0;
 }
 
-.ProseMirror ol,
-.ProseMirror ul {
+.sd-editor-scoped .ProseMirror ol,
+.sd-editor-scoped .ProseMirror ul {
   padding-inline-start: 0;
   padding-left: 0;
   list-style: none;
 }
 
-.ProseMirror li::marker {
+.sd-editor-scoped .ProseMirror li::marker {
   content: none;
 }
 
-.ProseMirror li::marker {
+.sd-editor-scoped .ProseMirror li::marker {
   padding: 0;
   margin: 0;
 }
 
-.ProseMirror li > p {
+.sd-editor-scoped .ProseMirror li > p {
   margin: 0;
   padding: 0;
   display: inline-block;
@@ -56,44 +59,44 @@
  * Hide marker for indented lists.
  * If a list-item contains a list but doesn't contain a "p" tag with text.
  */
-.ProseMirror ol {
+.sd-editor-scoped .ProseMirror ol {
   margin: 0;
 }
-.ProseMirror li:has(> ul:first-child, > ol:first-child):not(:has(> p)) {
+.sd-editor-scoped .ProseMirror li:has(> ul:first-child, > ol:first-child):not(:has(> p)) {
   list-style-type: none;
 }
 
-.ProseMirror li:has(> ul:first-child, > ol:first-child):not(:has(> p))::marker {
+.sd-editor-scoped .ProseMirror li:has(> ul:first-child, > ol:first-child):not(:has(> p))::marker {
   content: '';
 }
 
-.ProseMirror-hideselection *::selection {
+.sd-editor-scoped .ProseMirror-hideselection *::selection {
   background: transparent;
 }
 
-.ProseMirror-hideselection *::-moz-selection {
+.sd-editor-scoped .ProseMirror-hideselection *::-moz-selection {
   background: transparent;
 }
 
-.ProseMirror-hideselection * {
+.sd-editor-scoped .ProseMirror-hideselection * {
   caret-color: transparent;
 }
 
 /* See https://github.com/ProseMirror/prosemirror/issues/1421#issuecomment-1759320191 */
-.ProseMirror [draggable][contenteditable='false'] {
+.sd-editor-scoped .ProseMirror [draggable][contenteditable='false'] {
   user-select: text;
 }
 
-.ProseMirror-selectednode {
+.sd-editor-scoped .ProseMirror-selectednode {
   outline: 2px solid #8cf;
 }
 
 /* Make sure li selections wrap around markers */
-li.ProseMirror-selectednode {
+.sd-editor-scoped li.ProseMirror-selectednode {
   outline: none;
 }
 
-li.ProseMirror-selectednode:after {
+.sd-editor-scoped li.ProseMirror-selectednode:after {
   content: '';
   position: absolute;
   left: -32px;
@@ -104,24 +107,24 @@ li.ProseMirror-selectednode:after {
   pointer-events: none;
 }
 
-.ProseMirror img {
+.sd-editor-scoped .ProseMirror img {
   height: auto;
   max-width: 100%;
 }
 
 /* Protect against generic img rules */
-img.ProseMirror-separator {
+.sd-editor-scoped img.ProseMirror-separator {
   display: inline !important;
   border: none !important;
   margin: 0 !important;
 }
 
-.ProseMirror .sd-editor-tab {
+.sd-editor-scoped .ProseMirror .sd-editor-tab {
   display: inline-block;
   vertical-align: text-bottom;
 }
 
-.ProseMirror u .sd-editor-tab {
+.sd-editor-scoped .ProseMirror u .sd-editor-tab {
   white-space: pre;
   border-bottom: 1px solid #000;
   margin-bottom: 1.5px;
@@ -132,12 +135,12 @@ Tables
 https://github.com/ProseMirror/prosemirror-tables/blob/master/style/tables.css
 https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
 */
-.ProseMirror.resize-cursor {
+.sd-editor-scoped .ProseMirror.resize-cursor {
   cursor: ew-resize;
   cursor: col-resize;
 }
 
-.ProseMirror .tableWrapper {
+.sd-editor-scoped .ProseMirror .tableWrapper {
   --table-border-width: 1px;
   --offset: 2px;
 
@@ -151,7 +154,7 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   width: calc(100% + (var(--table-border-width) + var(--offset)));
 }
 
-.ProseMirror table {
+.sd-editor-scoped .ProseMirror table {
   border-collapse: collapse;
   border-spacing: 0;
   table-layout: auto;
@@ -159,12 +162,12 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   /* width: 100%; */
 }
 
-.ProseMirror tr {
+.sd-editor-scoped .ProseMirror tr {
   position: relative;
 }
 
-.ProseMirror td,
-.ProseMirror th {
+.sd-editor-scoped .ProseMirror td,
+.sd-editor-scoped .ProseMirror th {
   min-width: 0;
   position: relative;
   vertical-align: top;
@@ -172,24 +175,24 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   overflow-wrap: anywhere;
 }
 
-.ProseMirror td[data-placeholder],
-.ProseMirror th[data-placeholder] {
+.sd-editor-scoped .ProseMirror td[data-placeholder],
+.sd-editor-scoped .ProseMirror th[data-placeholder] {
   padding: 0 !important;
   border: 0 !important;
   background: transparent !important;
 }
 
-.ProseMirror td[data-placeholder] > *,
-.ProseMirror th[data-placeholder] > * {
+.sd-editor-scoped .ProseMirror td[data-placeholder] > *,
+.sd-editor-scoped .ProseMirror th[data-placeholder] > * {
   display: none !important;
 }
 
-.ProseMirror th {
+.sd-editor-scoped .ProseMirror th {
   font-weight: bold;
   text-align: left;
 }
 
-.ProseMirror table .column-resize-handle {
+.sd-editor-scoped .ProseMirror table .column-resize-handle {
   position: absolute;
   right: -2px;
   top: 0;
@@ -200,7 +203,7 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   pointer-events: none;
 }
 
-.ProseMirror table .selectedCell:after {
+.sd-editor-scoped .ProseMirror table .selectedCell:after {
   position: absolute;
   content: '';
   left: 0;
@@ -214,24 +217,24 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
 /* Tables - end */
 
 /* Track changes */
-.ProseMirror .track-insert-dec,
-.ProseMirror .track-delete-dec,
-.ProseMirror .track-format-dec {
+.sd-editor-scoped .ProseMirror .track-insert-dec,
+.sd-editor-scoped .ProseMirror .track-delete-dec,
+.sd-editor-scoped .ProseMirror .track-format-dec {
   pointer-events: none;
 }
 
-.ProseMirror .track-insert-dec.hidden,
-.ProseMirror .track-delete-dec.hidden {
+.sd-editor-scoped .ProseMirror .track-insert-dec.hidden,
+.sd-editor-scoped .ProseMirror .track-delete-dec.hidden {
   display: none;
 }
 
-.ProseMirror .track-insert-dec.highlighted {
+.sd-editor-scoped .ProseMirror .track-insert-dec.highlighted {
   border-top: 1px dashed var(--sd-track-insert-border, #00853d);
   border-bottom: 1px dashed var(--sd-track-insert-border, #00853d);
   background-color: var(--sd-track-insert-bg, #399c7222);
 }
 
-.ProseMirror .track-delete-dec.highlighted {
+.sd-editor-scoped .ProseMirror .track-delete-dec.highlighted {
   border-top: 1px dashed var(--sd-track-delete-border, #cb0e47);
   border-bottom: 1px dashed var(--sd-track-delete-border, #cb0e47);
   background-color: var(--sd-track-delete-bg, #cb0e4722);
@@ -239,21 +242,21 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   text-decoration-thickness: 2px !important;
 }
 
-.ProseMirror .track-format-dec.highlighted {
+.sd-editor-scoped .ProseMirror .track-format-dec.highlighted {
   border-bottom: 2px solid var(--sd-track-format-border, gold);
 }
 
-.ProseMirror .track-delete-widget {
+.sd-editor-scoped .ProseMirror .track-delete-widget {
   visibility: hidden;
 }
 /* Track changes - end */
 
 /* Collaboration cursors */
-.ProseMirror > .ProseMirror-yjs-cursor:first-child {
+.sd-editor-scoped .ProseMirror > .ProseMirror-yjs-cursor:first-child {
   margin-top: 16px;
 }
 
-.ProseMirror-yjs-cursor {
+.sd-editor-scoped .ProseMirror-yjs-cursor {
   position: relative;
   margin-left: -1px;
   margin-right: -1px;
@@ -264,7 +267,7 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   pointer-events: none;
 }
 
-.ProseMirror-yjs-cursor > div {
+.sd-editor-scoped .ProseMirror-yjs-cursor > div {
   position: absolute;
   top: -1.05em;
   left: -1px;
@@ -323,7 +326,7 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
 /* Presentation Editor Remote Cursors - end */
 
 /* Footnotes */
-.sd-footnote-ref {
+.sd-editor-scoped .sd-footnote-ref {
   font-size: 0.75em;
   line-height: 1;
   vertical-align: super;
@@ -331,13 +334,13 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
 }
 
 /* Image placeholder */
-.ProseMirror placeholder {
+.sd-editor-scoped .ProseMirror placeholder {
   display: inline;
   border: 1px solid #ccc;
   color: #ccc;
 }
 
-.ProseMirror placeholder:after {
+.sd-editor-scoped .ProseMirror placeholder:after {
   content: '☁';
   font-size: 200%;
   line-height: 0.1;
@@ -345,41 +348,41 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
 }
 
 /* Gapcursor */
-.ProseMirror-gapcursor {
+.sd-editor-scoped .ProseMirror-gapcursor {
   display: none;
   pointer-events: none;
   position: absolute;
   margin: 0;
 }
 
-.ProseMirror-gapcursor:after {
+.sd-editor-scoped .ProseMirror-gapcursor:after {
   content: '';
   display: block;
   position: absolute;
   top: -2px;
   width: 20px;
   border-top: 1px solid black;
-  animation: ProseMirror-cursor-blink 1.1s steps(2, start) infinite;
+  animation: superdoc-cursor-blink 1.1s steps(2, start) infinite;
 }
 
-@keyframes ProseMirror-cursor-blink {
+@keyframes superdoc-cursor-blink {
   to {
     visibility: hidden;
   }
 }
 
-.ProseMirror-focused .ProseMirror-gapcursor {
+.sd-editor-scoped .ProseMirror-focused .ProseMirror-gapcursor {
   display: block;
 }
 
-.ProseMirror div[data-type='contentBlock'] {
+.sd-editor-scoped .ProseMirror div[data-type='contentBlock'] {
   position: absolute;
   outline: none;
   user-select: none;
   z-index: -1;
 }
 
-.ProseMirror div[data-horizontal-rule='true'] {
+.sd-editor-scoped .ProseMirror div[data-horizontal-rule='true'] {
   position: relative;
   z-index: auto;
   display: inline-block;
@@ -388,23 +391,23 @@ https://github.com/ProseMirror/prosemirror-tables/blob/master/demo/index.html
   align-self: flex-end;
 }
 
-.sd-editor-dropcap {
+.sd-editor-scoped .sd-editor-dropcap {
   float: left;
   display: flex;
   align-items: baseline;
   margin-top: -5px;
 }
 
-.ProseMirror-search-match {
+.sd-editor-scoped .ProseMirror-search-match {
   background-color: #ffff0054;
 }
-.ProseMirror-active-search-match {
+.sd-editor-scoped .ProseMirror-active-search-match {
   background-color: #ff6a0054;
 }
-.ProseMirror span.sd-custom-selection::selection {
+.sd-editor-scoped .ProseMirror span.sd-custom-selection::selection {
   background: transparent;
 }
-.sd-custom-selection {
+.sd-editor-scoped .sd-custom-selection {
   background-color: #d9d9d9;
   border-radius: 0.1em;
 }
diff --git a/packages/super-editor/src/assets/styles/extensions/document-section.css b/packages/super-editor/src/assets/styles/extensions/document-section.css
index 1e55c9d160..6511e0c3e0 100644
--- a/packages/super-editor/src/assets/styles/extensions/document-section.css
+++ b/packages/super-editor/src/assets/styles/extensions/document-section.css
@@ -1,10 +1,10 @@
-.sd-document-section-block {
+.super-editor .sd-document-section-block {
   background-color: #fafafa;
   border: 1px solid #ababab;
   border-radius: 4px;
   position: relative;
 }
-.sd-document-section-block-info {
+.super-editor .sd-document-section-block-info {
   position: absolute;
   top: -19px;
   left: -1px;
@@ -22,27 +22,27 @@
   background-color: #fafafa;
 }
 
-.sd-document-section-block:hover {
+.super-editor .sd-document-section-block:hover {
   border-radius: 0 4px 4px 4px;
 }
 
-.sd-document-section-block:hover .sd-document-section-block-info {
+.super-editor .sd-document-section-block:hover .sd-document-section-block-info {
   display: flex;
   align-items: center;
 }
 
-.sd-document-section-block-info span {
+.super-editor .sd-document-section-block-info span {
   max-width: 100%;
   overflow: hidden;
   white-space: nowrap;
   text-overflow: ellipsis;
 }
 
-.ProseMirror.view-mode .sd-document-section-block {
+.super-editor .ProseMirror.view-mode .sd-document-section-block {
   background: none;
   border: none;
 }
 
-.ProseMirror.view-mode .sd-document-section-block-info {
+.super-editor .ProseMirror.view-mode .sd-document-section-block-info {
   display: none;
 }
diff --git a/packages/super-editor/src/assets/styles/extensions/noderesizer.css b/packages/super-editor/src/assets/styles/extensions/noderesizer.css
index 3f9990925a..c256c40d74 100644
--- a/packages/super-editor/src/assets/styles/extensions/noderesizer.css
+++ b/packages/super-editor/src/assets/styles/extensions/noderesizer.css
@@ -1,12 +1,12 @@
 /* Resize handles container */
-.sd-editor-resize-container {
+.sd-editor-resize-container.sd-editor-scoped {
   position: absolute;
   pointer-events: none;
   z-index: 11;
 }
 
 /* Resize handles */
-.sd-editor-resize-handle {
+.sd-editor-scoped .sd-editor-resize-handle {
   position: absolute;
   width: 12px;
   height: 12px;
@@ -18,53 +18,53 @@
   transition: all 0.1s ease;
 }
 
-.sd-editor-resize-handle:hover {
+.sd-editor-scoped .sd-editor-resize-handle:hover {
   background-color: #228be6;
   transform: scale(1.1);
   box-shadow: 0 0 6px rgba(0, 0, 0, 0.4);
 }
 
 /* Handle positions */
-.sd-editor-resize-handle-nw {
+.sd-editor-scoped .sd-editor-resize-handle-nw {
   top: -6px;
   left: -6px;
   cursor: nwse-resize;
 }
 
-.sd-editor-resize-handle-ne {
+.sd-editor-scoped .sd-editor-resize-handle-ne {
   top: -6px;
   right: -6px;
   cursor: nesw-resize;
 }
 
-.sd-editor-resize-handle-sw {
+.sd-editor-scoped .sd-editor-resize-handle-sw {
   bottom: -6px;
   left: -6px;
   cursor: nesw-resize;
 }
 
-.sd-editor-resize-handle-se {
+.sd-editor-scoped .sd-editor-resize-handle-se {
   bottom: -6px;
   right: -6px;
   cursor: nwse-resize;
 }
 
 /* Hide handles when editor loses focus */
-.ProseMirror:not(.ProseMirror-focused) .sd-editor-resize-container {
+.sd-editor-scoped .ProseMirror:not(.ProseMirror-focused) .sd-editor-resize-container {
   display: none;
 }
 
 /* Smooth transitions for resizing */
-.sd-editor-resizable-wrapper * {
+.sd-editor-scoped .sd-editor-resizable-wrapper * {
   transition: none;
 }
 
-.sd-editor-resizable-wrapper *:not([style*='width']) {
+.sd-editor-scoped .sd-editor-resizable-wrapper *:not([style*='width']) {
   transition: all 0.2s ease;
 }
 
 /* Resize feedback indicator */
-.sd-editor-resizable-wrapper::after {
+.sd-editor-scoped .sd-editor-resizable-wrapper::after {
   content: 'Drag corners to resize';
   position: absolute;
   bottom: -25px;
@@ -82,6 +82,6 @@
   z-index: 12;
 }
 
-.sd-editor-resizable-wrapper:hover::after {
+.sd-editor-scoped .sd-editor-resizable-wrapper:hover::after {
   opacity: 1;
 }
diff --git a/packages/super-editor/src/assets/styles/extensions/structured-content.css b/packages/super-editor/src/assets/styles/extensions/structured-content.css
index 4fbd438271..8d80d5d434 100644
--- a/packages/super-editor/src/assets/styles/extensions/structured-content.css
+++ b/packages/super-editor/src/assets/styles/extensions/structured-content.css
@@ -1,5 +1,5 @@
-.sd-structured-content,
-.sd-structured-content-block {
+.super-editor .sd-structured-content,
+.super-editor .sd-structured-content-block {
   padding: 1px;
   box-sizing: border-box;
   border-radius: 4px;
@@ -7,24 +7,24 @@
   position: relative;
 }
 
-.sd-structured-content:has(img),
-.sd-structured-content:has(img) .sd-structured-content__content {
+.super-editor .sd-structured-content:has(img),
+.super-editor .sd-structured-content:has(img) .sd-structured-content__content {
   display: inline-block;
 }
 
 /* Hover (not selected): light grey background, no handle */
-.sd-structured-content:not(.ProseMirror-selectednode):hover,
-.sd-structured-content-block:not(.ProseMirror-selectednode):hover {
+.super-editor .sd-structured-content:not(.ProseMirror-selectednode):hover,
+.super-editor .sd-structured-content-block:not(.ProseMirror-selectednode):hover {
   background-color: #f2f2f2;
 }
 
 /* Selected: border + handle visible */
-.sd-structured-content.ProseMirror-selectednode,
-.sd-structured-content-block.ProseMirror-selectednode {
+.super-editor .sd-structured-content.ProseMirror-selectednode,
+.super-editor .sd-structured-content-block.ProseMirror-selectednode {
   border-color: #629be7;
 }
 
-.sd-structured-content-draggable {
+.super-editor .sd-structured-content-draggable {
   font-size: 10px;
   align-items: center;
   justify-content: center;
@@ -46,7 +46,7 @@
   display: none;
 }
 
-.sd-structured-content-draggable span {
+.super-editor .sd-structured-content-draggable span {
   max-width: 100%;
   overflow: hidden;
   white-space: nowrap;
@@ -54,18 +54,18 @@
 }
 
 /* Handle only visible when selected */
-.sd-structured-content.ProseMirror-selectednode .sd-structured-content-draggable,
-.sd-structured-content-block.ProseMirror-selectednode .sd-structured-content-draggable {
+.super-editor .sd-structured-content.ProseMirror-selectednode .sd-structured-content-draggable,
+.super-editor .sd-structured-content-block.ProseMirror-selectednode .sd-structured-content-draggable {
   display: inline-flex;
 }
 
-.ProseMirror.view-mode .sd-structured-content,
-.ProseMirror.view-mode .sd-structured-content-block {
+.super-editor .ProseMirror.view-mode .sd-structured-content,
+.super-editor .ProseMirror.view-mode .sd-structured-content-block {
   padding: 0;
   border: none;
 }
 
-.ProseMirror.view-mode .sd-structured-content-draggable {
+.super-editor .ProseMirror.view-mode .sd-structured-content-draggable {
   display: none;
 }
 
diff --git a/packages/super-editor/src/assets/styles/layout/global.css b/packages/super-editor/src/assets/styles/layout/global.css
index 503c5885fe..ba6b428a27 100644
--- a/packages/super-editor/src/assets/styles/layout/global.css
+++ b/packages/super-editor/src/assets/styles/layout/global.css
@@ -11,10 +11,6 @@
   outline: none;
 }
 
-a {
-  text-decoration: auto;
-}
-
 .super-editor a {
   color: initial;
   text-decoration: auto;
diff --git a/packages/super-editor/src/tests/css-no-bleed.test.js b/packages/super-editor/src/tests/css-no-bleed.test.js
new file mode 100644
index 0000000000..a79b41af3d
--- /dev/null
+++ b/packages/super-editor/src/tests/css-no-bleed.test.js
@@ -0,0 +1,263 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync, readdirSync } from 'fs';
+import { resolve, join } from 'path';
+
+/**
+ * CSS Bleed Prevention Tests (SD-1850)
+ *
+ * Structural lint tests that parse CSS files and verify no selectors
+ * can bleed into host applications. This prevents regressions if someone
+ * adds an unscoped selector in the future.
+ */
+
+const SUPER_EDITOR_STYLES_DIR = resolve(__dirname, '../assets/styles');
+
+/**
+ * Recursively find all .css files in a directory.
+ */
+function findCssFiles(dir, prefix = '') {
+  const results = [];
+  for (const entry of readdirSync(dir, { withFileTypes: true })) {
+    const rel = prefix ? `${prefix}/${entry.name}` : entry.name;
+    if (entry.isDirectory()) {
+      results.push(...findCssFiles(join(dir, entry.name), rel));
+    } else if (entry.name.endsWith('.css')) {
+      results.push(rel);
+    }
+  }
+  return results;
+}
+
+/**
+ * Parse top-level CSS selectors from a CSS file string.
+ * Returns an array of selector strings (only top-level, not inside @media/@keyframes).
+ */
+function extractTopLevelSelectors(cssText) {
+  const selectors = [];
+  let depth = 0;
+  let current = '';
+  let inComment = false;
+  let inAtRule = false;
+
+  for (let i = 0; i < cssText.length; i++) {
+    const char = cssText[i];
+    const next = cssText[i + 1];
+
+    // Track comments
+    if (!inComment && char === '/' && next === '*') {
+      inComment = true;
+      i++;
+      continue;
+    }
+    if (inComment && char === '*' && next === '/') {
+      inComment = false;
+      i++;
+      continue;
+    }
+    if (inComment) continue;
+
+    // Track @ rules (keyframes, media, etc.)
+    if (depth === 0 && char === '@') {
+      inAtRule = true;
+      current = '@';
+      continue;
+    }
+
+    if (char === '{') {
+      if (depth === 0) {
+        const trimmed = current.trim();
+        if (trimmed && !inAtRule) {
+          // Split comma-separated selectors
+          const parts = trimmed.split(',').map((s) => s.trim());
+          selectors.push(...parts);
+        }
+        current = '';
+      }
+      depth++;
+      continue;
+    }
+
+    if (char === '}') {
+      depth--;
+      if (depth === 0) {
+        inAtRule = false;
+        current = '';
+      }
+      continue;
+    }
+
+    if (depth === 0) {
+      current += char;
+    }
+  }
+
+  return selectors;
+}
+
+/**
+ * Bare HTML element selectors that should NEVER appear at top-level without a parent scope.
+ * These are the most dangerous: they affect all elements of that type on the page.
+ */
+const BARE_ELEMENT_PATTERN =
+  /^(a|p|div|span|table|tr|td|th|ul|ol|li|h[1-6]|img|pre|blockquote|code|input|button|select|textarea|form|label|section|article|nav|header|footer|main|aside)\s*(\{|,|:|\[|>|\+|~|$)/;
+
+/**
+ * Check if a selector is scoped under a SuperDoc parent class.
+ */
+function isScopedSelector(selector) {
+  // Already scoped under .super-editor, .superdoc, .sd-, .presentation-editor, .tippy-box
+  const scopedPrefixes = ['.super-editor', '.superdoc', '.sd-', '.presentation-editor', '.tippy-box'];
+
+  return scopedPrefixes.some((prefix) => selector.startsWith(prefix));
+}
+
+describe('CSS Bleed Prevention (SD-1850)', () => {
+  it('should not have bare HTML element selectors at top level', () => {
+    const cssFiles = findCssFiles(SUPER_EDITOR_STYLES_DIR);
+    const violations = [];
+
+    for (const file of cssFiles) {
+      const fullPath = join(SUPER_EDITOR_STYLES_DIR, file);
+      const cssText = readFileSync(fullPath, 'utf8');
+      const selectors = extractTopLevelSelectors(cssText);
+
+      for (const selector of selectors) {
+        if (BARE_ELEMENT_PATTERN.test(selector)) {
+          violations.push({ file, selector });
+        }
+      }
+    }
+
+    if (violations.length > 0) {
+      const message = violations.map((v) => `  ${v.file}: "${v.selector}"`).join('\n');
+      expect.fail(
+        `Found bare HTML element selectors that will bleed into host apps:\n${message}\n\nScope them under .super-editor (e.g., ".super-editor a { ... }")`,
+      );
+    }
+  });
+
+  it('should scope all .ProseMirror selectors under .super-editor', () => {
+    const cssFiles = findCssFiles(SUPER_EDITOR_STYLES_DIR);
+    const violations = [];
+
+    for (const file of cssFiles) {
+      const fullPath = join(SUPER_EDITOR_STYLES_DIR, file);
+      const cssText = readFileSync(fullPath, 'utf8');
+      const selectors = extractTopLevelSelectors(cssText);
+
+      for (const selector of selectors) {
+        // Check for .ProseMirror selectors not scoped under .super-editor
+        const isProseMirrorSelector =
+          selector.startsWith('.ProseMirror') ||
+          selector.startsWith('li.ProseMirror') ||
+          selector.startsWith('img.ProseMirror');
+
+        if (isProseMirrorSelector && !selector.startsWith('.super-editor')) {
+          // Allow .ProseMirror inside already-scoped selectors (e.g., .superdoc-field .ProseMirror)
+          if (!isScopedSelector(selector)) {
+            violations.push({ file, selector });
+          }
+        }
+      }
+    }
+
+    if (violations.length > 0) {
+      const message = violations.map((v) => `  ${v.file}: "${v.selector}"`).join('\n');
+      expect.fail(
+        `Found .ProseMirror selectors not scoped under .super-editor:\n${message}\n\nPrefix with ".super-editor" (e.g., ".super-editor .ProseMirror { ... }")`,
+      );
+    }
+  });
+
+  it('should not have generic utility class names at top level', () => {
+    const cssFiles = findCssFiles(SUPER_EDITOR_STYLES_DIR);
+    const violations = [];
+
+    // Generic class names that are commonly used by frameworks (Bootstrap, Tailwind, etc.)
+    const genericClassNames = ['.sr-only', '.visually-hidden', '.hidden', '.clearfix', '.container', '.row', '.col'];
+
+    for (const file of cssFiles) {
+      const fullPath = join(SUPER_EDITOR_STYLES_DIR, file);
+      const cssText = readFileSync(fullPath, 'utf8');
+      const selectors = extractTopLevelSelectors(cssText);
+
+      for (const selector of selectors) {
+        for (const generic of genericClassNames) {
+          if (
+            selector === generic ||
+            selector.startsWith(generic + ' ') ||
+            selector.startsWith(generic + ':') ||
+            selector.startsWith(generic + '.')
+          ) {
+            violations.push({ file, selector, generic });
+          }
+        }
+      }
+    }
+
+    if (violations.length > 0) {
+      const message = violations.map((v) => `  ${v.file}: "${v.selector}" (conflicts with "${v.generic}")`).join('\n');
+      expect.fail(
+        `Found generic utility class names that will conflict with host app frameworks:\n${message}\n\nPrefix with "superdoc-" or "sd-" namespace`,
+      );
+    }
+  });
+
+  it('extractTopLevelSelectors should parse basic CSS correctly', () => {
+    const css = `
+      .foo { color: red; }
+      .bar, .baz { color: blue; }
+      @keyframes spin { to { transform: rotate(360deg); } }
+      .qux { color: green; }
+    `;
+    const selectors = extractTopLevelSelectors(css);
+    expect(selectors).toContain('.foo');
+    expect(selectors).toContain('.bar');
+    expect(selectors).toContain('.baz');
+    expect(selectors).toContain('.qux');
+    // @keyframes should not produce selectors
+    expect(selectors).not.toContain('@keyframes spin');
+  });
+
+  it('extractTopLevelSelectors should ignore nested selectors', () => {
+    const css = `
+      .parent {
+        .child { color: red; }
+      }
+      a { color: blue; }
+    `;
+    const selectors = extractTopLevelSelectors(css);
+    expect(selectors).toContain('.parent');
+    expect(selectors).toContain('a');
+    // .child is nested, should not appear
+    expect(selectors).not.toContain('.child');
+  });
+
+  it("should namespace all @keyframes names with superdoc- or sd-", () => {
+    const cssFiles = findCssFiles(SUPER_EDITOR_STYLES_DIR);
+    const violations = [];
+
+    for (const file of cssFiles) {
+      const fullPath = join(SUPER_EDITOR_STYLES_DIR, file);
+      const cssText = readFileSync(fullPath, "utf8");
+      const keyframePattern = /@keyframes\s+([\w-]+)/g;
+      let match;
+
+      while ((match = keyframePattern.exec(cssText)) !== null) {
+        const name = match[1];
+        if (!name.startsWith("superdoc-") && !name.startsWith("sd-")) {
+          violations.push({ file, keyframe: name });
+        }
+      }
+    }
+
+    if (violations.length > 0) {
+      const message = violations
+        .map((v) => `  ${v.file}: @keyframes ${v.keyframe}`)
+        .join("\n");
+      expect.fail(
+        `Found @keyframes names not prefixed with "superdoc-" or "sd-":\n${message}\n\nRename to start with "superdoc-" or "sd-" to avoid collisions with host apps`,
+      );
+    }
+  });
+});
diff --git a/packages/super-editor/src/tests/css-scoping-regressions.test.js b/packages/super-editor/src/tests/css-scoping-regressions.test.js
index 4a3cdd7ad2..c61180e206 100644
--- a/packages/super-editor/src/tests/css-scoping-regressions.test.js
+++ b/packages/super-editor/src/tests/css-scoping-regressions.test.js
@@ -177,4 +177,43 @@ describe('CSS Scoping Regressions', () => {
       host.remove();
     }
   });
+
+  it('noderesizer stylesheet should define overlay selectors that do not require .super-editor ancestry', () => {
+    const cssText = readFileSync(NODE_RESIZER_CSS_PATH, 'utf8');
+    const selectors = extractTopLevelSelectors(cssText);
+
+    const overlayContainerSelectors = selectors.filter(
+      (selector) =>
+        selector.includes('.sd-editor-resize-container') && !selector.includes(':hover') && !selector.includes('::'),
+    );
+    const overlayHandleSelectors = selectors.filter(
+      (selector) =>
+        selector.includes('.sd-editor-resize-handle') && !selector.includes(':hover') && !selector.includes('::'),
+    );
+
+    expect(overlayContainerSelectors.length).toBeGreaterThan(0);
+    expect(overlayHandleSelectors.length).toBeGreaterThan(0);
+    expect(overlayContainerSelectors.some((selector) => !selector.includes('.super-editor'))).toBe(true);
+    expect(overlayHandleSelectors.some((selector) => !selector.includes('.super-editor'))).toBe(true);
+  });
+
+  it('prosemirror stylesheet should define core selectors that do not require .super-editor ancestry', () => {
+    const cssText = readFileSync(PROSEMIRROR_CSS_PATH, 'utf8');
+    const selectors = extractTopLevelSelectors(cssText);
+
+    const proseMirrorRootSelectors = selectors.filter(targetsProseMirrorRoot);
+    const proseMirrorListSelectors = selectors.filter(
+      (selector) => selector.includes('.ProseMirror ol') || selector.includes('.ProseMirror ul'),
+    );
+    const proseMirrorSelectedNodeSelectors = selectors.filter((selector) =>
+      selector.includes('.ProseMirror-selectednode'),
+    );
+
+    expect(proseMirrorRootSelectors.length).toBeGreaterThan(0);
+    expect(proseMirrorListSelectors.length).toBeGreaterThan(0);
+    expect(proseMirrorSelectedNodeSelectors.length).toBeGreaterThan(0);
+    expect(proseMirrorRootSelectors.some((selector) => !selector.includes('.super-editor'))).toBe(true);
+    expect(proseMirrorListSelectors.some((selector) => !selector.includes('.super-editor'))).toBe(true);
+    expect(proseMirrorSelectedNodeSelectors.some((selector) => !selector.includes('.super-editor'))).toBe(true);
+  });
 });