<filter-function> includes url(), blur(), brightness(), contrast(), drop-shadow(), grayscale(), hue-rotate(), invert(), opacity(), saturate(), and sepia().
This experimental property applies effects like blurring or color shifting to an element before it is displayed.
Originally filter was an Internet Explorer proprietary property in IE5.5 to IE9 (it was removed in IE10). This IE proprietary property is now considered obsolete and should no longer be used. Use the "new" non-proprietary filter property instead, but note that it is still considered experimental at the time of this writing.