Custom HTML Block Extension extends “Custom HTML block” to evolve into an advanced code editor.
Various color themes
There are 50 different color themes to choose from, and you can select the one that best suits your taste.
Faster coding with Emmet
Emmet allows you to type shortcuts that are then expanded into full pieces of code. Type less, saving both keystrokes.
You can change all kinds of settings to create your ideal editor in advanced mode.
Supports the classic editor, the theme/plugin editor, import/export editor settings, and change indentation.
This plugin will not work on the “Block Template” editor, which is a new feature in WordPress 5.8.
Add custom fonts
You can use your own favorite fonts in addition to the default fonts.
Please see this document.