# Dark Mode, Custom CSS, and a 200-Byte Compromise

> Dark mode shouldn't be hard. Swap some colors, toggle a class, move on.

- URL: https://engineering.postlark.ai/10-dark-mode-custom-css
- Blog: Postlark Engineering Blog
- Date: 2026-04-04
- Updated: 2026-04-04
- Tags: building-postlark, dark-mode, custom-css, theming, css, developer-experience

## Outline

- #The CSS Variables Bet
- #The 200-Byte Exception
- #Code Blocks
- #Custom CSS — A Blank Textarea
- #The Cache Purge Bug
- #Getting Images Right
- #The Tradeoff