Fix wrong hover color in SL theme.

services/web/public/stylesheets/core/_common-variables.less

@@ -893,7 +893,7 @@
 @toolbar-header-shadow         : 0 0 2px #ccc;
 @toolbar-btn-color             : @link-color;
 @toolbar-btn-hover-color       : @link-hover-color;
-@toolbar-btn-hover-bg-color    : @link-hover-color;
+@toolbar-btn-hover-bg-color    : darken(white, 10%);
 @toolbar-btn-hover-text-shadow : 0 1px 0 rgba(0, 0, 0, 0.15);
 @toolbar-btn-active-color      : white;
 @toolbar-btn-active-bg-color   : @link-color;