diff --git a/browser/components/MarkdownEditor.js b/browser/components/MarkdownEditor.js
index 2bd5d951..2a1016cb 100644
--- a/browser/components/MarkdownEditor.js
+++ b/browser/components/MarkdownEditor.js
@@ -296,6 +296,8 @@ class MarkdownEditor extends React.Component {
           showCopyNotification={config.ui.showCopyNotification}
           storagePath={storage.path}
           noteKey={noteKey}
+          customCSS={config.preview.customCSS}
+          allowCustomCSS={config.preview.allowCustomCSS}
         />
       </div>
     )
diff --git a/browser/components/MarkdownPreview.js b/browser/components/MarkdownPreview.js
index 104ea708..89f71a9b 100755
--- a/browser/components/MarkdownPreview.js
+++ b/browser/components/MarkdownPreview.js
@@ -32,7 +32,7 @@ const CSS_FILES = [
   `${appPath}/node_modules/codemirror/lib/codemirror.css`
 ]
 
-function buildStyle (fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme) {
+function buildStyle (fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme, allowCustomCSS, customCSS) {
   return `
 @font-face {
   font-family: 'Lato';
@@ -62,7 +62,9 @@ function buildStyle (fontFamily, fontSize, codeBlockFontFamily, lineNumber, scro
        url('${appPath}/resources/fonts/MaterialIcons-Regular.woff') format('woff'),
        url('${appPath}/resources/fonts/MaterialIcons-Regular.ttf') format('truetype');
 }
+${allowCustomCSS ? customCSS : ''}
 ${markdownStyle}
+
 body {
   font-family: '${fontFamily.join("','")}';
   font-size: ${fontSize}px;
@@ -209,9 +211,9 @@ export default class MarkdownPreview extends React.Component {
 
   handleSaveAsHtml () {
     this.exportAsDocument('html', (noteContent, exportTasks) => {
-      const {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme} = this.getStyleParams()
+      const {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme, allowCustomCSS, customCSS} = this.getStyleParams()
 
-      const inlineStyles = buildStyle(fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme)
+      const inlineStyles = buildStyle(fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme, allowCustomCSS, customCSS)
       let body = this.markdown.render(escapeHtmlCharacters(noteContent))
 
       const files = [this.GetCodeThemeLink(codeBlockTheme), ...CSS_FILES]
@@ -347,14 +349,16 @@ export default class MarkdownPreview extends React.Component {
       prevProps.lineNumber !== this.props.lineNumber ||
       prevProps.showCopyNotification !== this.props.showCopyNotification ||
       prevProps.theme !== this.props.theme ||
-      prevProps.scrollPastEnd !== this.props.scrollPastEnd) {
+      prevProps.scrollPastEnd !== this.props.scrollPastEnd ||
+      prevProps.allowCustomCSS !== this.props.allowCustomCSS ||
+      prevProps.customCSS !== this.props.customCSS) {
       this.applyStyle()
       this.rewriteIframe()
     }
   }
 
   getStyleParams () {
-    const { fontSize, lineNumber, codeBlockTheme, scrollPastEnd, theme } = this.props
+    const { fontSize, lineNumber, codeBlockTheme, scrollPastEnd, theme, allowCustomCSS, customCSS } = this.props
     let { fontFamily, codeBlockFontFamily } = this.props
     fontFamily = _.isString(fontFamily) && fontFamily.trim().length > 0
         ? fontFamily.split(',').map(fontName => fontName.trim()).concat(defaultFontFamily)
@@ -363,14 +367,14 @@ export default class MarkdownPreview extends React.Component {
         ? codeBlockFontFamily.split(',').map(fontName => fontName.trim()).concat(defaultCodeBlockFontFamily)
         : defaultCodeBlockFontFamily
 
-    return {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme}
+    return {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme, allowCustomCSS, customCSS}
   }
 
   applyStyle () {
-    const {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme} = this.getStyleParams()
+    const {fontFamily, fontSize, codeBlockFontFamily, lineNumber, codeBlockTheme, scrollPastEnd, theme, allowCustomCSS, customCSS} = this.getStyleParams()
 
     this.getWindow().document.getElementById('codeTheme').href = this.GetCodeThemeLink(codeBlockTheme)
-    this.getWindow().document.getElementById('style').innerHTML = buildStyle(fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme)
+    this.getWindow().document.getElementById('style').innerHTML = buildStyle(fontFamily, fontSize, codeBlockFontFamily, lineNumber, scrollPastEnd, theme, allowCustomCSS, customCSS)
   }
 
   GetCodeThemeLink (theme) {
diff --git a/browser/components/MarkdownSplitEditor.js b/browser/components/MarkdownSplitEditor.js
index 2bee5c24..7016d0f4 100644
--- a/browser/components/MarkdownSplitEditor.js
+++ b/browser/components/MarkdownSplitEditor.js
@@ -141,6 +141,8 @@ class MarkdownSplitEditor extends React.Component {
           showCopyNotification={config.ui.showCopyNotification}
           storagePath={storage.path}
           noteKey={noteKey}
+          customCSS={config.preview.customCSS}
+          allowCustomCSS={config.preview.allowCustomCSS}
        />
       </div>
     )
diff --git a/browser/main/lib/ConfigManager.js b/browser/main/lib/ConfigManager.js
index 228692d6..908b243e 100644
--- a/browser/main/lib/ConfigManager.js
+++ b/browser/main/lib/ConfigManager.js
@@ -59,6 +59,8 @@ export const DEFAULT_CONFIG = {
     scrollPastEnd: false,
     smartQuotes: true,
     breaks: true,
+    allowCustomCSS: false,
+    customCSS: '',
     sanitize: 'STRICT' // 'STRICT', 'ALLOW_STYLES', 'NONE'
   },
   blog: {
diff --git a/browser/main/modals/PreferencesModal/UiTab.js b/browser/main/modals/PreferencesModal/UiTab.js
index e059d72d..e14f2279 100644
--- a/browser/main/modals/PreferencesModal/UiTab.js
+++ b/browser/main/modals/PreferencesModal/UiTab.js
@@ -28,6 +28,8 @@ class UiTab extends React.Component {
 
   componentDidMount () {
     CodeMirror.autoLoadMode(this.codeMirrorInstance.getCodeMirror(), 'javascript')
+    CodeMirror.autoLoadMode(this.customCSSCM.getCodeMirror(), 'css')
+    this.customCSSCM.getCodeMirror().setSize('400px', '400px')
     this.handleSettingDone = () => {
       this.setState({UiAlert: {
         type: 'success',
@@ -98,7 +100,9 @@ class UiTab extends React.Component {
         scrollPastEnd: this.refs.previewScrollPastEnd.checked,
         smartQuotes: this.refs.previewSmartQuotes.checked,
         breaks: this.refs.previewBreaks.checked,
-        sanitize: this.refs.previewSanitize.value
+        sanitize: this.refs.previewSanitize.value,
+        allowCustomCSS: this.refs.previewAllowCustomCSS.checked,
+        customCSS: this.customCSSCM.getCodeMirror().getValue()
       }
     }
 
@@ -159,6 +163,7 @@ class UiTab extends React.Component {
     const { config, codemirrorTheme } = this.state
     const codemirrorSampleCode = 'function iamHappy (happy) {\n\tif (happy) {\n\t  console.log("I am Happy!")\n\t} else {\n\t  console.log("I am not Happy!")\n\t}\n};'
     const enableEditRulersStyle = config.editor.enableRulers ? 'block' : 'none'
+    const customCSS = config.preview.customCSS
     return (
       <div styleName='root'>
         <div styleName='group'>
@@ -569,6 +574,20 @@ class UiTab extends React.Component {
               />
             </div>
           </div>
+          <div styleName='group-section'>
+            <div styleName='group-section-label'>
+              {i18n.__('Custom CSS')}
+            </div>
+            <div styleName='group-section-control'>
+              <input onChange={(e) => this.handleUIChange(e)}
+                checked={config.preview.allowCustomCSS}
+                ref='previewAllowCustomCSS'
+                type='checkbox'
+              />&nbsp;
+              {i18n.__('Allow custom CSS for preview')}
+              <ReactCodeMirror onChange={e => this.handleUIChange(e)} ref={e => (this.customCSSCM = e)} value={config.preview.customCSS} options={{ lineNumbers: true, mode: 'css', theme: codemirrorTheme }} />
+            </div>
+          </div>
 
           <div styleName='group-control'>
             <button styleName='group-control-rightButton'