Broken Categories' icon (conflicting CSS)

Problem/Motivation

If you remove these lines of CSS it looks fine instead (the background-image: url(../icons/taxonomy.svg); won't be overridden):

.toolbar .toolbar-bar .toolbar-menu-administration .menu-item .toolbar-icon-admin-toolbar-content-menu-linkscategories::before {
   -webkit-mask-image: url(../icons/gin/tags.svg) !important;
   mask-image: url(../icons/gin/tags.svg) !important;
}

I'm not sure if they are needed elsewhere though, please review.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes