you can set Opera to a dark design
options -> browser -> scroll down about half way to "user interface" -> toggle "dark design"

If you use tree tabs you can also change the appearance of the add-on bar on the left.

I now have a truly dark design of Opera. Some of the V7 add-ons also support a dark design, like "V7 bookmarks", see their add-on options

Active Stylus input on my ACER Switch Alpha 12 does not work as in any other application. In fact Opera is the only application that does something like this.

You have to double tab for the UI to register anything, sometimes it doesn't react at all and behaves weirdly (tabs getting dragged a little and staying in location preventing further interactions).

Some buttons like the x to close do never work with stylus input.

I was hoping to switch from Firefox to Opera for both my desktop and the touch notebook (firefox is terrible for touch input on a high dpi screen)