I downloaded some themes from the Chrome Web Store. Is there any way I can edit these themes?
(I want to change colors, buttons etc.)
If yes, how? If no, why?
A theme is a special kind of extension that changes the way the browser looks. Themes are packaged like regular extensions, but they don't contain JavaScript or HTML code. You can download any theme and modify it by editing the manifest.json file.
Colors are in RGB format. To find the strings you can use within the "colors" field, look for kColor* strings in theme_service.cc. Image resources use paths relative to the root of the extension. You can override any of the images that are specified by kThemeableImages in theme_service.cc. Just remove the "IDR_" and convert the remaining characters to lowercase.