Need guidelines for Angular Material menus, dropdowns, autocomplete, etc.

We have many points in the application where a menu or something like a drop down is created by Angular material, but the styles for these are not consistent.

**Menu**

The best looking template would be (in my opinion) the style of the menus, for example, when using the triple dot or the account circle:

It's changed from the default Angular Material menu in the following points:
- rounded
- removed paddings
- added colors (customizable)
- font-size 14px and font letter-spacing normal

**Autocomplete (without styles from menu)**

Autocomplete without any styling applied has a different font-size and letter-spacing, and padding on top and bottom.

Search bar:

Metadata persons and institutions:

**Autocomplete (with styles from menu)**

Removing the padding and making the font-size the same as the search bar looks better (in my opinion).

We could theoretically also make the options tighter, to fit more content at once.

**Selection dropdown (without styles from menu)**

Can be seen in visibility dialog and explore filters.

**Selection dropdown (with styles from menu)**

Looks better again (in my opinion), but I don't think changing the height of the options makes sense for these

No files or tests are named. Start by locating the Angular Material menu, autocomplete, and selection-dropdown usages in the search bar, metadata persons and institutions, visibility dialog, and explore filters. Compare their current styles with the examples and define a consistent result for menus, autocompletes, and selection dropdowns.

Written by the indexing model from the issue text.