Highlight hovered items in context/popup menus

[weeman1337]

Description

At the moment hovering an item in a context/popup menu doesn't highlight it.
This makes it hard to follow what action I am pointing at.

For example this menu:

Steps to reproduce

• Click the "…" (three dots) next to any message
• Hover the items

Current behaviour:

• The UI state does not change

Better behaviour:

• The item hovered gets highlighted so I know what I am going to click
• An SCSS variable for this already exists

Version information

• Platform: web

[weeman1337]

Closed in favour of #16182