Add Custom CSS Option

lib/main.coffee

@@ -27,6 +27,10 @@ module.exports =
     openPreviewInSplitPane:
       type: 'boolean'
       default: true
+    customCSSFile:
+      title: 'Custom CSS File'
+      type: 'string'
+      default: ''
     grammars:
       type: 'array'
       default: [

lib/renderer.coffee

@@ -47,6 +47,14 @@ render = (text, filePath, callback) ->
 
     html = sanitize(html)
     html = resolveImagePaths(html, filePath)
+
+    customCSSPath = atom.config.get('markdown-preview.customCSSFile')
+    if customCSSPath
+      customCSSPath = customCSSPath
+        .replace(/^~?\//, (process.env.HOME or '')+'/')
+      customCSS = fs.readFileSync(customCSSPath, 'utf8')
+      html += "<style>#{customCSS}</style>"
+
     callback(null, html.trim())
 
 sanitize = (html) ->