diff --git a/lib/load-paths-handler.coffee b/lib/load-paths-handler.coffee
new file mode 100644
index 0000000..6dcfbb7
--- /dev/null
+++ b/lib/load-paths-handler.coffee
@@ -0,0 +1,107 @@
+async = require 'async'
+fs = require 'fs'
+path = require 'path'
+{GitRepository} = require 'atom'
+{Minimatch} = require 'minimatch'
+
+PathsChunkSize = 10
+emittedPaths = new Set
+
+class PathLoader
+  constructor: (@rootPath, ignoreVcsIgnores, @traverseSymlinkDirectories, @ignoredNames, @extensions) ->
+    @paths = []
+    @realPathCache = {}
+    @repo = null
+    if ignoreVcsIgnores
+      repo = GitRepository.open(@rootPath, refreshOnWindowFocus: false)
+      @repo = repo if repo?.relativize(path.join(@rootPath, 'test')) is 'test'
+
+  load: (done) ->
+    @loadPath @rootPath, =>
+      @flushPaths()
+      @repo?.destroy()
+      done()
+
+  isIgnored: (loadedPath) ->
+    relativePath = path.relative(@rootPath, loadedPath)
+    if @repo?.isPathIgnored(relativePath)
+      true
+    else
+      for ignoredName in @ignoredNames
+        return true if ignoredName.match(relativePath)
+
+  pathLoaded: (loadedPath, done) ->
+    badExtension = path.extname(loadedPath).toLowerCase() not in @extensions
+    unless @isIgnored(loadedPath) or emittedPaths.has(loadedPath) or badExtension
+      @paths.push(loadedPath)
+      emittedPaths.add(loadedPath)
+
+    if @paths.length is PathsChunkSize
+      @flushPaths()
+    done()
+
+  flushPaths: ->
+    emit('load-stylesheets:stylesheets-found', @paths)
+    @paths = []
+
+  loadPath: (pathToLoad, done) ->
+    return done() if @isIgnored(pathToLoad)
+    fs.lstat pathToLoad, (error, stats) =>
+      return done() if error?
+      if stats.isSymbolicLink()
+        @isInternalSymlink pathToLoad, (isInternal) =>
+          return done() if isInternal
+          fs.stat pathToLoad, (error, stats) =>
+            return done() if error?
+            if stats.isFile()
+              @pathLoaded(pathToLoad, done)
+            else if stats.isDirectory()
+              if @traverseSymlinkDirectories
+                @loadFolder(pathToLoad, done)
+              else
+                done()
+            else
+              done()
+      else if stats.isDirectory()
+        @loadFolder(pathToLoad, done)
+      else if stats.isFile()
+        @pathLoaded(pathToLoad, done)
+      else
+        done()
+
+  loadFolder: (folderPath, done) ->
+    fs.readdir folderPath, (error, children=[]) =>
+      async.each(
+        children,
+        (childName, next) =>
+          @loadPath(path.join(folderPath, childName), next)
+        done
+      )
+
+  isInternalSymlink: (pathToLoad, done) ->
+    fs.realpath pathToLoad, @realPathCache, (err, realPath) =>
+      if err
+        done(false)
+      else
+        done(realPath.search(@rootPath) is 0)
+
+module.exports = (rootPaths, followSymlinks, ignoreVcsIgnores, ignores=[], extensions) ->
+  ignoredNames = []
+  for ignore in ignores when ignore
+    try
+      ignoredNames.push(new Minimatch(ignore, matchBase: true, dot: true))
+    catch error
+      console.warn "Error parsing ignore pattern (#{ignore}): #{error.message}"
+
+  async.each(
+    rootPaths,
+    (rootPath, next) ->
+      new PathLoader(
+        rootPath,
+        ignoreVcsIgnores,
+        followSymlinks,
+        ignoredNames,
+        extensions
+      ).load(next)
+    @async()
+  )
diff --git a/lib/main.coffee b/lib/main.coffee
index 2696398..78bbda8 100644
--- a/lib/main.coffee
+++ b/lib/main.coffee
@@ -3,4 +3,6 @@ provider = require './provider'
 module.exports =
   activate: -> provider.loadCompletions()
 
+  deactivate: -> provider.deactivate()
+
   getProvider: -> provider
diff --git a/lib/provider.coffee b/lib/provider.coffee
index 08512a4..3741d80 100644
--- a/lib/provider.coffee
+++ b/lib/provider.coffee
@@ -1,5 +1,6 @@
 fs = require 'fs'
 path = require 'path'
+{CompositeDisposable, Task} = require 'atom'
 
 trailingWhitespace = /\s$/
 attributePattern = /\s+([a-zA-Z][-a-zA-Z]*)\s*=\s*$/
@@ -8,6 +9,11 @@ tagPattern = /<([a-zA-Z][-a-zA-Z]*)(?:\s|$)/
 module.exports =
   selector: '.text.html'
   disableForSelector: '.text.html .comment'
+  cssClassScope: 'entity.other.attribute-name.class.css'
+  cssIdScope: 'entity.other.attribute-name.id.css'
+  cssClassAttr: 'class'
+  cssIdAttr: 'id'
+  cssFileExtensions: ['.css', '.scss', '.less', '.html']
   filterSuggestions: true
 
   getSuggestions: (request) ->
@@ -133,7 +139,11 @@ module.exports =
       @buildAttributeValueCompletion(tag, attribute, value)
 
   buildAttributeValueCompletion: (tag, attribute, value) ->
-    if @completions.attributes[attribute].global
+    if attribute in [@cssClassAttr, @cssIdAttr]
+      text: value.value
+      type: attribute
+      description: "From #{atom.project.relativizePath(value.path)[1]}"
+    else if @completions.attributes[attribute].global
       text: value
       type: 'value'
       description: "#{value} value for global #{attribute} attribute"
@@ -145,11 +155,20 @@ module.exports =
       descriptionMoreURL: @getLocalAttributeDocsURL(attribute, tag)
 
   loadCompletions: ->
+    @disposables = new CompositeDisposable
     @completions = {}
+    @cssCompletions = []
     fs.readFile path.resolve(__dirname, '..', 'completions.json'), (error, content) =>
       @completions = JSON.parse(content) unless error?
       return
 
+    atom.workspace.observeTextEditors (editor) =>
+      @disposables.add editor.onDidSave (e) =>
+        if path.extname(e.path).toLowerCase() in @cssFileExtensions
+          @cssCompletions = @cssCompletions.filter (c) -> c.path isnt e.path
+          @updateCSSCompletionsFromFile(e.path)
+    @pathLoader()
+
   getPreviousTag: (editor, bufferPosition) ->
     {row} = bufferPosition
     while row >= 0
@@ -168,7 +187,40 @@ module.exports =
 
     attributePattern.exec(line)?[1]
 
+  updateCSSCompletionsFromFile: (fileName) ->
+    content = fs.readFileSync(fileName, 'utf-8')
+    grammar = atom.grammars.selectGrammar(fileName)
+    for line in grammar.tokenizeLines(content)
+      for token in line
+        [..., scope] = token.scopes
+        if scope in [@cssClassScope, @cssIdScope]
+          @cssCompletions.push
+            path: fileName
+            scope: scope
+            value: token.value
+
+  pathLoader: ->
+    fileNames = []
+
+    followSymlinks = atom.config.get 'core.followSymlinks'
+    ignoredNames = atom.config.get('core.ignoredNames') ? []
+    ignoreVcsIgnores = atom.config.get('core.excludeVcsIgnoredPaths')
+
+    taskPath = require.resolve('./load-paths-handler')
+
+    task = Task.once taskPath, atom.project.getPaths(), followSymlinks,
+      ignoreVcsIgnores, ignoredNames, @cssFileExtensions, =>
+        for f in fileNames
+          @updateCSSCompletionsFromFile(f)
+
+    task.on 'load-stylesheets:stylesheets-found', (paths) ->
+      fileNames.push(paths...)
+
   getAttributeValues: (attribute) ->
+    if attribute?.toLowerCase() is @cssClassAttr
+      return (c for c in @cssCompletions when c.scope is @cssClassScope)
+    else if attribute?.toLowerCase() is @cssIdAttr
+      return (c for c in @cssCompletions when c.scope is @cssIdScope)
     attribute = @completions.attributes[attribute]
     attribute?.attribOption ? []
 
@@ -184,5 +236,9 @@ module.exports =
   getGlobalAttributeDocsURL: (attribute) ->
     "https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/#{attribute}"
 
+  deactivate: ->
+    @disposables.dispose()
+
 firstCharsEqual = (str1, str2) ->
+  str1 = str1?.value or str1
   str1[0].toLowerCase() is str2[0].toLowerCase()
diff --git a/package.json b/package.json
index 21c84c0..2b60d02 100644
--- a/package.json
+++ b/package.json
@@ -17,6 +17,11 @@
   },
   "devDependencies": {
     "coffeelint": "^1.9.7",
-    "request": "^2.53.0"
+    "request": "^2.53.0",
+    "temp": "^0.8.3"
+  },
+  "dependencies": {
+    "async": "^1.5.1",
+    "minimatch": "^3.0.0"
   }
 }
diff --git a/spec/provider-spec.coffee b/spec/provider-spec.coffee
index 883b3b1..5624155 100644
--- a/spec/provider-spec.coffee
+++ b/spec/provider-spec.coffee
@@ -1,3 +1,7 @@
+fs = require 'fs'
+path = require 'path'
+temp = require 'temp'
+
 describe "HTML autocompletions", ->
   [editor, provider] = []
 
@@ -283,3 +287,56 @@ describe "HTML autocompletions", ->
     args = atom.commands.dispatch.mostRecentCall.args
     expect(args[0].tagName.toLowerCase()).toBe 'atom-text-editor'
     expect(args[1]).toBe 'autocomplete-plus:activate'
+
+describe "CSS completions inside of HTML attributes", ->
+  [editor, provider] = []
+
+  getCompletions = ->
+    cursor = editor.getLastCursor()
+    start = cursor.getBeginningOfCurrentWordBufferPosition()
+    end = cursor.getBufferPosition()
+    prefix = editor.getTextInRange([start, end])
+    request =
+      editor: editor
+      bufferPosition: end
+      scopeDescriptor: cursor.getScopeDescriptor()
+      prefix: prefix
+    provider.getSuggestions(request)
+
+  beforeEach ->
+    waitsForPromise -> atom.packages.activatePackage('autocomplete-html')
+    waitsForPromise -> atom.packages.activatePackage('language-html')
+    waitsForPromise -> atom.packages.activatePackage('language-css')
+
+    runs ->
+      provider = atom.packages.getActivePackage('autocomplete-html').mainModule.getProvider()
+
+    projectDir = fs.realpathSync(temp.mkdirSync('atom-project'))
+    samplePath = path.join(projectDir, 'sample.html')
+    fs.writeFileSync(samplePath, """<html>
+      <style>
+        #test1 {}
+        .test2 {
+          font-size: 15px;
+        }
+      </style>
+      <div class="
+      <div id="
+      </html>""")
+
+    atom.project.setPaths([projectDir])
+    waitsForPromise -> atom.workspace.open(samplePath)
+    waitsFor -> provider.cssCompletions.length > 0
+    runs -> editor = atom.workspace.getActiveTextEditor()
+
+  it "autocompletes class names within open file", ->
+    editor.setCursorBufferPosition([7, 12])
+    completions = getCompletions()
+    expect(completions.length).toBe 1
+    expect(completions[0].text).toBe 'test2'
+
+  it "autocompletes ids within open file", ->
+    editor.setCursorBufferPosition([8, 9])
+    completions = getCompletions()
+    expect(completions.length).toBe 1
+    expect(completions[0].text).toBe 'test1'