by Andi Dittrich on WordPress.org
All-in-one Syntax Highlighting solution. Full Gutenberg and Classic Editor integration. Graphical theme customizer. Based on EnlighterJS.

HTML highlighting Example (Enlighter Theme)
Enlighter is a free, easy-to-use, syntax highlighting tool for WordPress. Highlighting is powered by the EnlighterJS javascript library to provide a beautiful code-appearance.
Using it can be as simple as adding a new Enlighter Sourcecode block (Gutenberg) and insert the code which you want to highlight: Enlighter takes care of the rest!
An easy to use Theme-Customizer is included to modify the build-in themes without any css knowlegde!
It also supports the automatic creation of tab-panes to display code-groups together (useful for multi-language examples – e.g. html+css+js)
tab key (single line and block selection)pre codeblocks)jQuery Ajax.loadJetpack.InfiniteScrollShortcodes are deprecated and should be used in text editor mode only – never use them within Gutenberg Editor or Classic Editor!
In case your language is not available try the Generic Mode which covers a lot of programming languages – or request a new language on GitHub
All modern webbrowsers with enabled Javascript and HTML5 capabilities for “data-” attributes are compatible with Enlighter. It’s possible that it may work with earlier/other browsers.