Fix invisible buttons in password fields (desktop Safari)

[Iksas]

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• I have made only one major change in my proposed changes.
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• I have tested my proposed changes.
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What does this PR aim to accomplish?:

When using dark themes in desktop Safari, the autofill button cannot be seen because it's colored black on a black background. For the same reason, the caps lock indicator cannot be seen. This PR fixes both issues.

How does this PR accomplish the above?:

The issues are fixed by using the text color for the autofill button, and by inverting the caps lock indicator:

What documentation changes (if any) are needed to support this PR?:

none

[yubiuser]

What's about the other themes? Do they offer an caps-lock indicator that needs to be fixed?

Are the indicators browser-dependent? I haven't seen them on Chrome or Firefox?

[Iksas]

You're right, all dark themes are affected. Don't know how I missed this, I have now fixed them all. The color of the password button is now the same as the text color.

The indicators are indeed browser-dependent. Desktop Safari is the only browser that I know of that has them.

Also, please let me know if I have added the fixes in the right lines. It was a bit hard to decide where to put them in default-dark.css

[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-v5-13-web-v5-10-and-core-v5-8-released/52254/1