Create new themes styles

Basics

In your css file you can import the default styling or start from the ground up,

@import 'default.css';

Change the background and default color,

[class*="shj-lang-"] {
	color: ...;
	background: ...;
	...
}

Change tokens style,

.shj-syn-[token-name] {color: ...}

Change line numbering style,

.shj-numbers {color: ...}

Change inline style,

code[class*="shj-lang-"] {...}

Change multiline style,

[class*="shj-lang-"]:not(code) {...}

Change the default header thing

[class*="shj-lang-"]:not(code):before {...}

Get creative

Feel free to get creative and change other more fancy things, And if you need more answer the default css file can maybe help you