diff --git a/src/components/Editor.tsx b/src/components/Editor.tsx
index a27d5ebb..2485cefb 100644
--- a/src/components/Editor.tsx
+++ b/src/components/Editor.tsx
@@ -5,7 +5,9 @@ import { createReactInlineContentSpec, useCreateBlockNote, SuggestionMenuControl
 import { BlockNoteView } from '@blocknote/mantine'
 import '@blocknote/mantine/style.css'
 import type { VaultEntry } from '../types'
+import { useEditorTheme } from '../hooks/useTheme'
 import './Editor.css'
+import './EditorTheme.css'
 
 interface Tab {
   entry: VaultEntry
@@ -163,6 +165,7 @@ function BlockNoteTab({ content, entries, onNavigateWikilink }: { content: strin
   const [, body] = useMemo(() => splitFrontmatter(content), [content])
   const navigateRef = useRef(onNavigateWikilink)
   navigateRef.current = onNavigateWikilink
+  const { cssVars } = useEditorTheme()
 
   const editor = useCreateBlockNote({ schema })
 
@@ -217,7 +220,7 @@ function BlockNoteTab({ content, entries, onNavigateWikilink }: { content: strin
   const isDark = typeof document !== 'undefined' && document.documentElement.getAttribute('data-theme') !== 'light'
 
   return (
-    <div className="editor__blocknote-container">
+    <div className="editor__blocknote-container" style={cssVars as React.CSSProperties}>
       <BlockNoteView
         editor={editor}
         theme={isDark ? 'dark' : 'light'}
diff --git a/src/components/EditorTheme.css b/src/components/EditorTheme.css
new file mode 100644
index 00000000..b50eb9e4
--- /dev/null
+++ b/src/components/EditorTheme.css
@@ -0,0 +1,179 @@
+/* ==============================================
+   EditorTheme.css — BlockNote theme overrides
+   Driven by CSS custom properties from theme.json
+   ============================================== */
+
+/* --- Editor root --- */
+.editor__blocknote-container .bn-editor {
+  font-family: var(--editor-font-family);
+  font-size: var(--editor-font-size);
+  line-height: var(--editor-line-height);
+  max-width: var(--editor-max-width);
+  padding: var(--editor-padding-vertical) var(--editor-padding-horizontal);
+  color: var(--colors-text);
+  caret-color: var(--colors-cursor);
+}
+
+.editor__blocknote-container .bn-editor ::selection {
+  background: var(--colors-selection);
+}
+
+/* --- Paragraph spacing --- */
+.editor__blocknote-container .bn-block-content[data-content-type="paragraph"] {
+  margin-bottom: var(--editor-paragraph-spacing);
+}
+
+/* --- Headings --- */
+.editor__blocknote-container [data-content-type="heading"][data-level="1"] .bn-inline-content {
+  font-size: var(--headings-h1-font-size);
+  font-weight: var(--headings-h1-font-weight);
+  line-height: var(--headings-h1-line-height);
+  color: var(--headings-h1-color);
+  letter-spacing: var(--headings-h1-letter-spacing);
+}
+.editor__blocknote-container [data-content-type="heading"][data-level="1"] {
+  margin-top: var(--headings-h1-margin-top);
+  margin-bottom: var(--headings-h1-margin-bottom);
+}
+
+.editor__blocknote-container [data-content-type="heading"][data-level="2"] .bn-inline-content {
+  font-size: var(--headings-h2-font-size);
+  font-weight: var(--headings-h2-font-weight);
+  line-height: var(--headings-h2-line-height);
+  color: var(--headings-h2-color);
+  letter-spacing: var(--headings-h2-letter-spacing);
+}
+.editor__blocknote-container [data-content-type="heading"][data-level="2"] {
+  margin-top: var(--headings-h2-margin-top);
+  margin-bottom: var(--headings-h2-margin-bottom);
+}
+
+.editor__blocknote-container [data-content-type="heading"][data-level="3"] .bn-inline-content {
+  font-size: var(--headings-h3-font-size);
+  font-weight: var(--headings-h3-font-weight);
+  line-height: var(--headings-h3-line-height);
+  color: var(--headings-h3-color);
+  letter-spacing: var(--headings-h3-letter-spacing);
+}
+.editor__blocknote-container [data-content-type="heading"][data-level="3"] {
+  margin-top: var(--headings-h3-margin-top);
+  margin-bottom: var(--headings-h3-margin-bottom);
+}
+
+.editor__blocknote-container [data-content-type="heading"][data-level="4"] .bn-inline-content {
+  font-size: var(--headings-h4-font-size);
+  font-weight: var(--headings-h4-font-weight);
+  line-height: var(--headings-h4-line-height);
+  color: var(--headings-h4-color);
+  letter-spacing: var(--headings-h4-letter-spacing);
+}
+.editor__blocknote-container [data-content-type="heading"][data-level="4"] {
+  margin-top: var(--headings-h4-margin-top);
+  margin-bottom: var(--headings-h4-margin-bottom);
+}
+
+/* --- Bullet lists --- */
+.editor__blocknote-container [data-content-type="bulletListItem"] {
+  padding-left: var(--lists-padding-left);
+  margin-bottom: var(--lists-item-spacing);
+}
+
+/* --- Numbered lists --- */
+.editor__blocknote-container [data-content-type="numberedListItem"] {
+  padding-left: var(--lists-padding-left);
+  margin-bottom: var(--lists-item-spacing);
+}
+
+/* --- Checkbox / check list items --- */
+.editor__blocknote-container [data-content-type="checkListItem"] {
+  margin-bottom: var(--lists-item-spacing);
+}
+
+/* --- Inline: bold --- */
+.editor__blocknote-container .bn-editor strong {
+  font-weight: var(--inline-styles-bold-font-weight);
+  color: var(--inline-styles-bold-color);
+}
+
+/* --- Inline: italic --- */
+.editor__blocknote-container .bn-editor em {
+  font-style: var(--inline-styles-italic-font-style);
+  color: var(--inline-styles-italic-color);
+}
+
+/* --- Inline: strikethrough --- */
+.editor__blocknote-container .bn-editor s,
+.editor__blocknote-container .bn-editor del {
+  color: var(--inline-styles-strikethrough-color);
+  text-decoration: var(--inline-styles-strikethrough-text-decoration);
+}
+
+/* --- Inline: code --- */
+.editor__blocknote-container .bn-editor code {
+  font-family: var(--inline-styles-code-font-family);
+  font-size: var(--inline-styles-code-font-size);
+  background-color: var(--inline-styles-code-background-color);
+  padding: var(--inline-styles-code-padding-vertical) var(--inline-styles-code-padding-horizontal);
+  border-radius: var(--inline-styles-code-border-radius);
+  color: var(--inline-styles-code-color);
+}
+
+/* --- Inline: links --- */
+.editor__blocknote-container .bn-editor a {
+  color: var(--inline-styles-link-color);
+  text-decoration: var(--inline-styles-link-text-decoration);
+}
+
+/* --- Wikilinks (override from Editor.css with theme vars) --- */
+.editor__blocknote-container .wikilink {
+  color: var(--inline-styles-wikilink-color);
+  text-decoration: var(--inline-styles-wikilink-text-decoration);
+  border-bottom: var(--inline-styles-wikilink-border-bottom);
+  cursor: var(--inline-styles-wikilink-cursor);
+}
+
+/* --- Code blocks --- */
+.editor__blocknote-container [data-content-type="codeBlock"] {
+  font-family: var(--code-blocks-font-family);
+  font-size: var(--code-blocks-font-size);
+  line-height: var(--code-blocks-line-height);
+  background-color: var(--code-blocks-background-color);
+  padding: var(--code-blocks-padding-vertical) var(--code-blocks-padding-horizontal);
+  border-radius: var(--code-blocks-border-radius);
+  margin-top: var(--code-blocks-margin-vertical);
+  margin-bottom: var(--code-blocks-margin-vertical);
+}
+
+/* --- Blockquote --- */
+.editor__blocknote-container [data-content-type="blockquote"],
+.editor__blocknote-container blockquote {
+  border-left: var(--blockquote-border-left-width) solid var(--blockquote-border-left-color);
+  padding-left: var(--blockquote-padding-left);
+  margin-top: var(--blockquote-margin-vertical);
+  margin-bottom: var(--blockquote-margin-vertical);
+  color: var(--blockquote-color);
+  font-style: var(--blockquote-font-style);
+}
+
+/* --- Table --- */
+.editor__blocknote-container [data-content-type="table"] table {
+  border-color: var(--table-border-color);
+  font-size: var(--table-font-size);
+}
+
+.editor__blocknote-container [data-content-type="table"] th {
+  background: var(--table-header-background);
+  padding: var(--table-cell-padding-vertical) var(--table-cell-padding-horizontal);
+}
+
+.editor__blocknote-container [data-content-type="table"] td {
+  padding: var(--table-cell-padding-vertical) var(--table-cell-padding-horizontal);
+  border-color: var(--table-border-color);
+}
+
+/* --- Horizontal rule --- */
+.editor__blocknote-container hr {
+  border: none;
+  border-top: var(--horizontal-rule-thickness) solid var(--horizontal-rule-color);
+  margin: var(--horizontal-rule-margin-vertical) 0;
+}
diff --git a/src/hooks/useTheme.ts b/src/hooks/useTheme.ts
new file mode 100644
index 00000000..c2877279
--- /dev/null
+++ b/src/hooks/useTheme.ts
@@ -0,0 +1,51 @@
+import { useMemo } from 'react'
+import themeConfig from '../theme.json'
+
+type ThemeValue = string | number | Record<string, unknown> | unknown[]
+
+/** Convert a nested theme config object into a flat map of CSS custom properties */
+function flattenTheme(
+  obj: Record<string, ThemeValue>,
+  prefix = '--'
+): Record<string, string> {
+  const result: Record<string, string> = {}
+
+  for (const [key, value] of Object.entries(obj)) {
+    const cssKey = `${prefix}${camelToKebab(key)}`
+
+    if (value === null || value === undefined) continue
+    if (Array.isArray(value)) continue // skip arrays (e.g. nestedBulletSymbols)
+
+    if (typeof value === 'object') {
+      Object.assign(result, flattenTheme(value as Record<string, ThemeValue>, `${cssKey}-`))
+    } else if (typeof value === 'number') {
+      // Numbers that look like px values get 'px' suffix; ratios/weights don't
+      // These are unitless values; everything else gets 'px'
+      const isUnitless = /weight|lineHeight|opacity/i.test(key) ||
+        cssKey.includes('line-height') ||
+        cssKey.includes('font-weight')
+      const needsPx = !isUnitless
+      result[cssKey] = needsPx ? `${value}px` : String(value)
+    } else {
+      result[cssKey] = String(value)
+    }
+  }
+
+  return result
+}
+
+function camelToKebab(str: string): string {
+  return str.replace(/([a-z0-9])([A-Z])/g, '$1-$2').toLowerCase()
+}
+
+export function useEditorTheme() {
+  const { cssVars, styleString } = useMemo(() => {
+    const vars = flattenTheme(themeConfig as Record<string, ThemeValue>)
+    const str = Object.entries(vars)
+      .map(([k, v]) => `${k}: ${v};`)
+      .join('\n')
+    return { cssVars: vars, styleString: str }
+  }, [])
+
+  return { themeConfig, cssVars, styleString }
+}
diff --git a/src/theme.json b/src/theme.json
new file mode 100644
index 00000000..ec37c55b
--- /dev/null
+++ b/src/theme.json
@@ -0,0 +1,137 @@
+{
+  "editor": {
+    "fontFamily": "'Inter', -apple-system, BlinkMacSystemFont, sans-serif",
+    "fontSize": 16,
+    "lineHeight": 1.7,
+    "maxWidth": 720,
+    "paddingHorizontal": 40,
+    "paddingVertical": 20,
+    "paragraphSpacing": 8
+  },
+  "headings": {
+    "h1": {
+      "fontSize": 32,
+      "fontWeight": 700,
+      "lineHeight": 1.2,
+      "marginTop": 32,
+      "marginBottom": 12,
+      "color": "var(--text-heading)",
+      "letterSpacing": -0.5
+    },
+    "h2": {
+      "fontSize": 24,
+      "fontWeight": 600,
+      "lineHeight": 1.3,
+      "marginTop": 28,
+      "marginBottom": 10,
+      "color": "var(--text-heading)",
+      "letterSpacing": -0.3
+    },
+    "h3": {
+      "fontSize": 20,
+      "fontWeight": 600,
+      "lineHeight": 1.4,
+      "marginTop": 24,
+      "marginBottom": 8,
+      "color": "var(--text-heading)",
+      "letterSpacing": 0
+    },
+    "h4": {
+      "fontSize": 17,
+      "fontWeight": 600,
+      "lineHeight": 1.4,
+      "marginTop": 20,
+      "marginBottom": 6,
+      "color": "var(--text-heading)",
+      "letterSpacing": 0
+    }
+  },
+  "lists": {
+    "bulletSymbol": "•",
+    "bulletSize": 14,
+    "bulletColor": "var(--text-tertiary)",
+    "indentSize": 24,
+    "itemSpacing": 4,
+    "paddingLeft": 8,
+    "nestedBulletSymbols": ["•", "◦", "▪"]
+  },
+  "checkboxes": {
+    "size": 16,
+    "borderRadius": 3,
+    "checkedColor": "var(--accent-blue)",
+    "uncheckedBorderColor": "var(--text-muted)"
+  },
+  "inlineStyles": {
+    "bold": {
+      "fontWeight": 700,
+      "color": "var(--text-primary)"
+    },
+    "italic": {
+      "fontStyle": "italic",
+      "color": "var(--text-primary)"
+    },
+    "strikethrough": {
+      "color": "var(--text-tertiary)",
+      "textDecoration": "line-through"
+    },
+    "code": {
+      "fontFamily": "'SF Mono', 'Fira Code', monospace",
+      "fontSize": 14,
+      "backgroundColor": "var(--bg-hover-subtle)",
+      "paddingHorizontal": 4,
+      "paddingVertical": 2,
+      "borderRadius": 3,
+      "color": "var(--text-secondary)"
+    },
+    "link": {
+      "color": "var(--accent-blue)",
+      "textDecoration": "underline"
+    },
+    "wikilink": {
+      "color": "var(--accent-blue)",
+      "textDecoration": "none",
+      "borderBottom": "1px dotted var(--accent-blue)",
+      "cursor": "pointer"
+    }
+  },
+  "codeBlocks": {
+    "fontFamily": "'SF Mono', 'Fira Code', monospace",
+    "fontSize": 13,
+    "lineHeight": 1.5,
+    "backgroundColor": "var(--bg-card)",
+    "paddingHorizontal": 16,
+    "paddingVertical": 12,
+    "borderRadius": 6,
+    "marginVertical": 12
+  },
+  "blockquote": {
+    "borderLeftWidth": 3,
+    "borderLeftColor": "var(--accent-blue)",
+    "paddingLeft": 16,
+    "marginVertical": 12,
+    "color": "var(--text-secondary)",
+    "fontStyle": "italic"
+  },
+  "table": {
+    "borderColor": "var(--border-primary)",
+    "headerBackground": "var(--bg-card)",
+    "cellPaddingHorizontal": 12,
+    "cellPaddingVertical": 8,
+    "fontSize": 14
+  },
+  "horizontalRule": {
+    "color": "var(--border-primary)",
+    "marginVertical": 24,
+    "thickness": 1
+  },
+  "colors": {
+    "background": "var(--bg-primary)",
+    "text": "var(--text-primary)",
+    "textSecondary": "var(--text-secondary)",
+    "textMuted": "var(--text-muted)",
+    "heading": "var(--text-heading)",
+    "accent": "var(--accent-blue)",
+    "selection": "var(--bg-selected)",
+    "cursor": "var(--text-primary)"
+  }
+}