Same game as rPe38f5457 but hadn't realized before:
IE5.5 to IE8 released 03/2009 supported the filter: alpha() syntax.
(IE8 and IE9 supported -ms-filter which was deprecated in IE9 and is unsupported since IE10 released 09/2012.)
See
- https://learn.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/platform-apis/ms532847(v=vs.85)
- https://learn.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/platform-apis/ms532967(v=vs.85)
- https://learn.microsoft.com/en-us/previous-versions/ms530752(v=vs.85)
- https://stackoverflow.com/questions/40389599/firefox-declaration-dropped-errors
filter is a valid standard CSS3 property unrelated to IE's obsolete filter: alpha() syntax.
Standard filter does not support alpha() per https://developer.mozilla.org/en-US/docs/Web/CSS/filter.
Thus modern browsers throw errors in the console to be avoided by removing this old syntax.
