Found built-in dark mode in Chromium
I asked the question of how to make dark mode in the browser, without plugins, but no one answered. I found the answer and decided to share it with you who don't know. You can enter the address in a new tab in Chromium chrome://flags/#enable-force-dark There you can choose from different modes.
Brave has a user setting to enable this.
I run this on my phone to conserve battery but colors are distorted/inverted with some graphics.
Thank you.