Adjust dropdown-toggle class on LCARS theme.

[rdwebdesign]

What does this PR aim to accomplish?

Adjust the .dropdown-toggle class, to better fit LCARS theme.

How does this PR accomplish the above?

Using darker colors and make the control fill the whole table cell.

Before:

After:

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[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-20-1-web-v5-18-1-and-core-v5-15-released/60495/1