Why the !important rule ? The need for that rule is very rare I don't think this is one of those cases. CSS cascades the rules down later rules overwrite earlier ones.
!important
Since this rule has the same "score" (or "weight") as the :hover rule for normal buttons, this should work just fine.
.es-toolbarButtonTool:hover, .es-toolbarDropdownTool:hover { border-color: #eeeeee; } .es-toolbarButtonTool-disabled:hover { border-color: transparent; }
(also spaces instead of tabs)
As soon as !important is used, it messes with all cascading rules that come after. Should be avoided at all costs.