[Data table] Multiple styling bugs

[shixiedesign]

All themes

1. Header row has extra border bottom. No border until the row immediately underneath header is selected.

2. Zebra row has wrong color

Correct zebra row background colors are:
Odd row background: $field-01 at 40% opacity
Even row background: $field-01

Current

Current dark theme zebra is all row colors wrong ⚠️

Should be

Dark themes only

1. Overflow menu hover background wrong

Should be using token $hover-selected-ui which is gray 70 hover in G90 theme

White theme	Gray 10 theme	Gray 90 theme	Gray 100 theme
gray-20 hover #cacaca	gray-20 hover #cacaca	gray-70 hover #656565	gray-80 hover #4c4c4c

Current:

Should be:

2. Overflow menu not using correct theme

For token spec, reference : #3213

Current:

Should be:

3. Setting (dependent on overflow?) menu is not getting the token assignment too

[asudoh]

1. The latest master has border on header row removed unless sticky header feature is enabled
2. Updating zebra color requires component-specific theme token (CC @emyarod), applying alpha channel to theme token (CSS custom properties) is hacky
3. fix(overflow-menu): update trigger's hover color #4270 fixes the color of overflow menu's trigger button and chore(devenv): apply theme custom properties to floating menus #3444 fixes the color of overflow menu body

@aagonzales Wrt 1. does it (the current behavior in master) sound good? Wrt 2., should we track the issue separately? Thanks!

[tw15egan]

Closing this as most of the issues have been fixed, and the zebra style fixes are being tracked in #3143