:future

擬似クラス :past, :future (選択子)

仕様書

[2] Selectors Level 4 ( ( 版)) <http://dev.w3.org/csswg/selectors4/#past-pseudo>

[3] Selectors Level 4 ( ( 版)) <http://dev.w3.org/csswg/selectors4/#future-pseudo>