* lisp/textmodes/css-mode.el (scss-mode): New major-mode.

* lisp/textmodes/css-mode.el (scss-mode): New major-mode.
(css-mode-syntax-table): Use d style comment, to ease the scss case.
(css-ident-re): Allow things like @-moz-keyframes.
(scss--hash-re): New const.
(css--font-lock-keywords): New function, extracted from
css-font-lock-keywords.
(css-font-lock-keywords): Use it.
(scss-mode-syntax-table, scss-font-lock-keywords): New vars.
(scss-smie--not-interpolation-p): New function.
(css-smie--forward-token, css-smie--backward-token): Use it.
(css-mode): Remove left-over code.
* test/indent/scss-mode.scss: New file.
* test/indent/css-mode.css: Add a few uneventful examples.