I made a Chrome theme.
I was hoping to get the window looking translucent, with the desktop wallpaper showing through with a blur,
but it turns out you can't tweak the look with CSS — instead you fill in values for properties in a JSON file. So I ended up making the images in Figma and working around it that way.
One thing I'm still stuck on: I can't figure out the property that controls the search bar icon's color, and it's hard to read as-is…… I'll update this once I find a fix.
To publish the theme I had to register as a Chrome developer, which cost $5 — cheaper than I expected, so that was nice.
I wrote up how I made it over on Zenn. It's simple enough that you could probably just check the official docs instead, but here it is anyway.