The 'about' screen is not readable on a 4K monitor
I have a 4K monitor and when I choose the Vivaldi main menu/help/about the about screen is so small you can not make it out
Is it substantially different than any other tab/webpage? (I'm thinking it must be or you wouldn't have posted). The font size on the About Version tab (Menu > Help > About) in every version I have used looks about the same as the text in the post editor where I'm typing right now, which is smaller than the font size in the post Preview or in an actual post, but still very readable.
If you happen to still be using Technical Preview 2, try updating to the most recent Developer snapshot.
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The problem is that the page cannot be zoomed like web pages.
If you do a find and replace in \Vivaldi\Application\18.104.22.168\resources\vivaldi\stylecommon.css for font-size and replace the values with new values 200% bigger, that should fix it for you.
I modified 11.5px to 15px, 9pix to 12pix, and 8pix to 11 pix. I am using Vivaldi on a 1920 x 1080 monitor at Windows display setting of 125%
Fixed in the 156 developer build
Still happens to me on my Retina MBP 13" on latest build 22.214.171.124
Doesn't happen on my Windows machine though.