Fix indentation rule in css-mode

* lisp/textmodes/css-mode.el (css-smie-rules): Fix indentation of
brackets in presence of pseudo-selectors.  (Bug#21328)

lisp/textmodes/css-mode.el

@@ -344,7 +344,7 @@
     (`(:elem . arg) 0)
     (`(:list-intro . ,(or `";" `"")) t) ;"" stands for BOB (bug#15467).
     (`(:before . "{")
-     (when (smie-rule-hanging-p)
+     (when (or (smie-rule-hanging-p) (smie-rule-bolp))
        (smie-backward-sexp ";")
        (smie-indent-virtual)))
     (`(:before . ,(or "{" "("))

test/indent/css-mode.css

@@ -36,3 +36,8 @@ a.b:c,d.e:f,g[h]:i,j[k]:l,.m.n:o,.p.q:r,.s[t]:u,.v[w]:x { /* bug:20282 */
 div.x3
 {
 }
+
+article:hover
+{
+    color: black;
+}