The custom HTML widget allows you to add html code to a widget. It has syntax highlighting, auto-complete and error detection.
Note: Javascript will be removed automatically from widgets when they are saved. This means if you try to use code provided that includes Javascript it will be removed.
This widget can be useful for services that allow provide html fragments to embed content. For example the Widget visible on this page is from clustermaps and shows the number of visitors.
<a href="https://clustrmaps.com/site/1c0w8" title="Visit tracker"><img src="//www.clustrmaps.com/map_v2.png?d=1ge4j7IhLgo2HYiqWwmhoW3YOkzwgF4hgwu10khPSIM&cl=ffffff" /></a>Block Editor
You can use Custom HTML block in the block editor too, here is a gif and below the results of the block:
