[css-images] Allow either order of <percentage> and <image> in cross-fade().

--HG--
extra : rebase_source : 4a2c84fe7eece6acf11974a98d8d984ea6278c0c
[mediaqueries] Make the general MQ railroad diagram correct.

--HG--
extra : rebase_source : b77421a6ad84a11b61491911e9f9ffa4f681033d