Microsoft has added new themes to the add-ons store for the Chromium-based Edge browser, giving users some more room for customization. Edge has supported Chrome themes for some time, but like all add-ons from outside Microsoft's own platform, you would need to manually enable the ability to install them from the browser settings.
There are over two dozen new themes available on the Edge add-ons store today, though Microsoft has previously released some celebratory ones, too. The one based on Wonder Woman 1984 was actually made available a while back to tie into the release of the movie, for example.
The majority of the themes available are based on Microsoft properties, more specifically Xbox games. There are themes based on Halo, Gears of War, Ori and the Will of the Wisps, and a few more titles. There are also some that are described as bringing the "delightful and eye-catching artwork of Microsoft 365" to the browser.
Of course, you can still install themes from the Chrome Web Store if Microsoft's offerings are too limited, and recently, Microsoft also added the ability to choose color-based themes right from the browser's settings, though this is still not widely available. If you want to check out the new Microsoft themes, you can do so here.