Hi.

The following patch adds support for completion at point to
`css-mode'.


 From e312007cab0bfc72b59bab16ca56d8c5f6e29fa8 Mon Sep 17 00:00:00 2001
 From: =?UTF-8?q?Simen=20Heggest=C3=B8yl?= <simenheg@gmail.com>
Date: Sat, 14 Mar 2015 11:05:55 +0100
Subject: [PATCH 2/3] Add support for completion in `css-mode'

* textmodes/css-mode.el (css--complete-property): New function for
completing CSS properties.
(css--complete-pseudo-element-or-class): New function for
completing CSS pseudo-elements and pseudo-classes.
(css--complete-at-rule): New function for completing CSS at-rules.
(css-completion-at-point): New function providing completion for
`css-mode'.
(css-mode): Add support for completion.
---
 lisp/ChangeLog             |  8 ++++++++
 lisp/textmodes/css-mode.el | 45 
+++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 70122c7..36a1f87 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -5,6 +5,14 @@
 	(css-pseudo-ids): Remove.
 	(css-pseudo-class-ids): New variable.
 	(css-pseudo-element-ids): New variable.
+	(css--complete-property): New function for completing CSS
+	properties.
+	(css--complete-pseudo-element-or-class): New function for
+	completing CSS pseudo-elements and pseudo-classes.
+	(css--complete-at-rule): New function for completing CSS at-rules.
+	(css-completion-at-point): New function providing completion for
+	`css-mode'.
+	(css-mode): Add support for completion.

 2015-03-13  Kevin Ryde  <user42_kevin@yahoo.com.au>

diff --git a/lisp/textmodes/css-mode.el b/lisp/textmodes/css-mode.el
index dc11d44..d467343 100644
--- a/lisp/textmodes/css-mode.el
+++ b/lisp/textmodes/css-mode.el
@@ -28,7 +28,7 @@

 ;; - electric ; and }
 ;; - filling code with auto-fill-mode
-;; - completion
+;; - attribute value completion
 ;; - fix font-lock errors with multi-line selectors

 ;;; Code:
@@ -345,6 +345,45 @@
     (`(:before . ,(or "{" "("))
      (if (smie-rule-hanging-p) (smie-rule-parent 0)))))

+;;; Completion
+
+(defun css--complete-property ()
+  "Complete property at point."
+  (save-excursion
+    (let ((pos (point)))
+      (skip-chars-backward "-[:alnum:]")
+      (let ((start (point)))
+        (skip-chars-backward " \t\r\n")
+        (when (memq (char-before) '(?\{ ?\;))
+          (list start pos css-property-ids))))))
+
+(defun css--complete-pseudo-element-or-class ()
+  "Complete pseudo-element or pseudo-class at point."
+  (save-excursion
+    (let ((pos (point)))
+      (skip-chars-backward "-[:alnum:]")
+      (when (eq (char-before) ?\:)
+        (list (point) pos
+              (if (eq (char-before (- (point) 1)) ?\:)
+                  css-pseudo-element-ids
+                css-pseudo-class-ids))))))
+
+(defun css--complete-at-rule ()
+  "Complete at-rule (statement beginning with `@') at point."
+  (save-excursion
+    (let ((pos (point)))
+      (skip-chars-backward "-[:alnum:]")
+      (when (eq (char-before) ?\@)
+        (list (point) pos css-at-ids)))))
+
+(defun css-completion-at-point ()
+  "Complete current symbol at point.
+Currently supports completion of CSS properties, pseudo-elements,
+pesudo-classes, and at-rules."
+  (or (css--complete-property)
+      (css--complete-pseudo-element-or-class)
+      (css--complete-at-rule)))
+
 ;;;###autoload
 (define-derived-mode css-mode fundamental-mode "CSS"
   "Major mode to edit Cascading Style Sheets."
@@ -360,7 +399,9 @@
               :forward-token #'css-smie--forward-token
               :backward-token #'css-smie--backward-token)
   (setq-local electric-indent-chars
-              (append css-electric-keys electric-indent-chars)))
+              (append css-electric-keys electric-indent-chars))
+  (add-hook 'completion-at-point-functions
+            #'css-completion-at-point nil 'local))

 (defvar comment-continue)

-- 
2.1.4