Microsoft Edge for all platforms added a Page Colors setting in the Fall, it affects it like Windows Contrast themes do. It has the same theme choices as Windows, plus "White." It doesn't have a UI for creating custom themes.
Firefox's Manage Colors setting also does `forced-colors`.
I collected information about testing the color and contrast user preferences on a page. The two above browser features are user-friendly ones, unlike the Chromium's emulators in the DevTools Rendering pane.
https://codepen.io/ccwilcox/full/YPzraqb
Mayank (npub1ftx…yzsr)