To darken the background of websites in Google Chrome on Android, you can use an experimental feature that forces all web content to appear in a dark theme. This feature is accessible through Chrome's flags settings. First, open Chrome and type chrome://flags into the address bar. Search for the flag labeled "Darken websites checkbox in theme setting" and set it to "Enabled". After relaunching Chrome, go to Settings > Theme. If you have selected "System default" or "Dark" as your theme, you will now see an option labeled "Darken websites". Enable this option to apply a dark theme to all websites, regardless of their original design. This feature is particularly useful for reducing eye strain in low-light environments and can help extend battery life on devices with OLED screens. Note that this is an experimental feature, and results may vary across different websites.