diff --git a/app/gui2/src/components/PlainTextEditor.vue b/app/gui2/src/components/PlainTextEditor.vue
index a8da56bf705..3395d58e5f4 100644
--- a/app/gui2/src/components/PlainTextEditor.vue
+++ b/app/gui2/src/components/PlainTextEditor.vue
@@ -22,7 +22,7 @@ const textSync: LexicalPlugin = {
   },
 }
 
-useLexical(contentElement, 'PlainTextEditor', [plainText, textSync])
+useLexical(contentElement, 'PlainTextEditor', {}, [plainText, textSync])
 </script>
 
 <template>
diff --git a/app/gui2/src/components/lexical/MarkdownEditorImpl.vue b/app/gui2/src/components/lexical/MarkdownEditorImpl.vue
index cd7df8762d1..de149272a56 100644
--- a/app/gui2/src/components/lexical/MarkdownEditorImpl.vue
+++ b/app/gui2/src/components/lexical/MarkdownEditorImpl.vue
@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { useLexical, type LexicalPlugin } from '@/components/lexical'
+import { lexicalTheme, useLexical, type LexicalPlugin } from '@/components/lexical'
 import FloatingSelectionMenu from '@/components/lexical/FloatingSelectionMenu.vue'
 import LexicalContent from '@/components/lexical/LexicalContent.vue'
 import SelectionFormattingToolbar from '@/components/lexical/SelectionFormattingToolbar.vue'
@@ -18,7 +18,7 @@ import {
 import { HeadingNode, QuoteNode, registerRichText } from '@lexical/rich-text'
 import { TableCellNode, TableNode, TableRowNode } from '@lexical/table'
 import { syncRef } from '@vueuse/core'
-import { shallowRef, type ComponentInstance } from 'vue'
+import { shallowRef, useCssModule, type ComponentInstance } from 'vue'
 
 const markdown = defineModel<string>({ required: true })
 
@@ -56,7 +56,8 @@ const markdownSyncPlugin: LexicalPlugin = {
   },
 }
 
-const { editor } = useLexical(contentElement, 'MarkdownEditor', [
+const theme = lexicalTheme(useCssModule('lexicalTheme'))
+const { editor } = useLexical(contentElement, 'MarkdownEditor', theme, [
   listPlugin,
   markdownPlugin,
   markdownSyncPlugin,
@@ -77,43 +78,6 @@ const formatting = useFormatting(editor)
 .fullHeight {
   height: 100%;
 }
-
-.LexicalContent :deep(h1) {
-  font-weight: 700;
-  font-size: 16px;
-  line-height: 1.75;
-}
-
-.LexicalContent :deep(h2, h3, h4, h5, h6) {
-  font-size: 14px;
-  line-height: 2;
-}
-
-.LexicalContent :deep(p + p) {
-  margin-bottom: 4px;
-}
-
-.LexicalContent :deep(ol) {
-  list-style-type: decimal;
-  list-style-position: outside;
-  padding-left: 1.6em;
-}
-
-.LexicalContent :deep(ul) {
-  list-style-type: disc;
-  list-style-position: outside;
-  padding-left: 1.6em;
-}
-
-.LexicalContent :deep(strong) {
-  font-weight: bold;
-}
-
-.LexicalContent :deep(.lexical-strikethrough) {
-  text-decoration: line-through;
-}
-
-.LexicalContent :deep(.lexical-italic) {
-  font-style: italic;
-}
 </style>
+
+<style module="lexicalTheme" src="@/components/lexical/theme.css" />
diff --git a/app/gui2/src/components/lexical/index.ts b/app/gui2/src/components/lexical/index.ts
index 5cd99e0965a..0a9e8bd2565 100644
--- a/app/gui2/src/components/lexical/index.ts
+++ b/app/gui2/src/components/lexical/index.ts
@@ -1,11 +1,13 @@
 import { unrefElement, type MaybeElement } from '@vueuse/core'
 import {
   createEditor,
+  type EditorThemeClasses,
   type KlassConstructor,
   type LexicalEditor,
   type LexicalNode,
   type LexicalNodeReplacement,
 } from 'lexical'
+import { assertDefined } from 'shared/util/assert'
 import { markRaw, onMounted, type Ref } from 'vue'
 
 type NodeDefinition = KlassConstructor<typeof LexicalNode> | LexicalNodeReplacement
@@ -15,9 +17,34 @@ export interface LexicalPlugin {
   register: (editor: LexicalEditor) => void
 }
 
+export function lexicalTheme(theme: Record<string, string>): EditorThemeClasses {
+  interface EditorThemeShape extends Record<string, EditorThemeShape | string> {}
+  const editorClasses: EditorThemeShape = {}
+  for (const [classPath, className] of Object.entries(theme)) {
+    const path = classPath.split('_')
+    const leaf = path.pop()
+    // `split` will always return at least one value
+    assertDefined(leaf)
+    let obj = editorClasses
+    for (const section of path) {
+      const nextObj = (obj[section] ??= {})
+      if (typeof nextObj === 'string') {
+        console.warn(
+          `Lexical theme contained path '${classPath}', but path component '${section}' is a leaf.`,
+        )
+        continue
+      }
+      obj = nextObj
+    }
+    obj[leaf] = className
+  }
+  return editorClasses
+}
+
 export function useLexical(
   contentElement: Ref<MaybeElement>,
   namespace: string,
+  theme: EditorThemeClasses,
   plugins: LexicalPlugin[],
 ) {
   const nodes = new Set<NodeDefinition>()
@@ -27,12 +54,7 @@ export function useLexical(
     createEditor({
       editable: true,
       namespace,
-      theme: {
-        text: {
-          strikethrough: 'lexical-strikethrough',
-          italic: 'lexical-italic',
-        },
-      },
+      theme,
       nodes: [...nodes],
       onError: console.error,
     }),
diff --git a/app/gui2/src/components/lexical/theme.css b/app/gui2/src/components/lexical/theme.css
new file mode 100644
index 00000000000..17de6d6458d
--- /dev/null
+++ b/app/gui2/src/components/lexical/theme.css
@@ -0,0 +1,52 @@
+/*
+Lexical theme. Class names are derived from the `LexicalThemeClasses` type from `lexical`, with the hierarchy flattened
+using `_` to separate levels. See the `lexicalTheme` function in `lexical/formatting.ts`.
+*/
+
+.heading_h1 {
+  font-weight: 700;
+  font-size: 20px;
+  line-height: 1.75;
+}
+.heading_h2 {
+  font-weight: 700;
+  font-size: 16px;
+  line-height: 1.75;
+}
+.heading_h3,
+.heading_h4,
+.heading_h5,
+.heading_h6 {
+  font-size: 14px;
+  line-height: 2;
+}
+
+.text_strikethrough {
+  text-decoration: line-through;
+}
+.text_italic {
+  font-style: italic;
+}
+.text_quote {
+  margin-left: 0.2em;
+  border-left: 0.3em solid #ccc;
+  padding-left: 1.6em;
+}
+.text_bold {
+  font-weight: bold;
+}
+
+.paragraph {
+  margin-bottom: 0.5em;
+}
+
+.list_ol {
+  list-style-type: decimal;
+  list-style-position: outside;
+  padding-left: 1.6em;
+}
+.list_ul {
+  list-style-type: disc;
+  list-style-position: outside;
+  padding-left: 1.6em;
+}