Add class to replace `options_ui` entirely

[fregante]

I think that options_ui is absolutely ugly on Chrome. The translucent background shows a bunch of UI that is irrelevant/useless to most users, resulting in plain noise.

From now on I'd just rather use options_page and then fake a similar style, something like this:

[fregante]

Possible useful styles:

background: radial-gradient(circle, rgb(161, 228, 255) 0%, rgba(255, 255, 255, 0.1) 70%),
radial-gradient(circle, rgb(55, 81, 213) 0%, rgba(255, 255, 255, 0.1) 65%);

 border-radius: 16px;
 box-shadow: rgba(0, 0, 0, 0.15) 15px 30px 80px;