How do I customise the look of update menus?

Hi there

How do I control the look of the update menus?


For example, say I wanted to change the shading of the menu item boxes to something else?

I have tried custom CSS like below but it does not seem to be working.

    fill: #e7e7e7;

Or change the look of the update menu container by making it 100% width with a border?

    border-bottom: 1px solid #e7e7e7;
    width: 100%;

Is it possible?

Any ideas please? Have had a good look on the forum and have noticed similar questions have gone unanswered. Surely it is possible?

I did not try (yet), but I saw some options here: