Midnight Lizard for Chrome, Firefox, and Edge provides a full-service extension/add-on for website color customization and more.

This really has a nice set of tools for creating color combos on the websites you visit; it also has many default color schemes available at the author's site. It also allows you to use different color schemes on each website. You can choose between dark, light, grayscale, or colorful color schemes to fit the lighting conditions. Midnight Lizard allows you to adjust brightness, saturation, contrast, hues easily, and increase contrast to make the text easier to read as well as highlighting hyperlinks to a custom color for improved accessibility and readability.

Midnight Lizard also includes Simplified Mode, which is meant to improve its performance on heavy websites and switch between websites blacklist and whitelist modes. There are so many combos for fine-tuning colors that you'll be able to decrease eyestrain on your long browser sessions.
 
Midnight Lizard Features:

Modify existing or create new color schemes
Increase contrast to make text easier to read
Apply blue light filter to shift all colors towards red light
Keep original images and hues without inversion
Schedule automatic activation and deactivation
Use keyboard shortcuts to toggle the extension/add-on
   -on current website: Alt+Shift+L
   -globally: Alt+Shift+M
Use with local HTML files
Shade bright colors and images
Change any color you want
Dynamically change browser theme (disabled by default)
Sync your settings
Configure background, text, buttons, links, borders, and images
Apply globally, per-website or with URL match patterns

Similar:
How to Enable Dark Mode in Windows 10
How to Enable Dark Mode for All Sites in Microsoft Edge
10 Google Chrome Flags to Improve Your Browsing Experience

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