I found Kindle's secret custom reading modes

There's no better feeling than finding a book you literally can't put down. The best plots don't care if it's 3AM on a weeknight, and your sleep schedule has likely suffered at the hands of a good story.

Source : https://www.pocket-lint.com/i-used-this-hack-to-create-a-custom-reading-mode-on-my-kindle-and-solve-my-biggest-problem/