Remove background opacity in menus; improving accessibility/readability

[artfulrobot]

Overview

Civi's menu is 90% opaque for some reason, presumably a stylistic decision. It makes it hard to read the menu items. This fixes that by making the menu opaque.

I found it hard to read and the idea of going opaque seemed to suit at least some others
https://chat.civicrm.org/civicrm/pl/cp98ne1isjbrtx41rgh936fejw

Before

After

[civibot]

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[colemanw]

Personally I thought the opacity was a nice touch. But if people hate it, ok we can do away with it.

[artfulrobot]

Thanks, @colemanw

I think if it would be fine if combined with a background blur so the text on top was still easy to read. My eyes aren't terrible but I have found it hard enough times to warrant this PR.

[mlutfy]

👍 I didn't want to bike-shed on the menu, but I've been patching it on our installs. (my eyes aren't very good and generally favour high contrast)

[artfulrobot]

Seems quite a lot of support for this.

TBH, I never had a problem when it was black 90% opaque. I suspect this is to do with the fact that our eyes are more sensitive to varations in bright colours than in dark colours.

[totten]

<bike-shed-data-point>I don't hate the transparency, and I do think it looks prettier to glance at, but it is harder for me to read, so soft +1 on tweaks to improve readability.</bike-shed-data-point>

[mlutfy]

I think there is sufficient consensus to merge this?