---
title: "Custom CSS"
canonical: "https://kb.uconn.edu/space/IKB/10814456015/Custom%20CSS"
format: markdown
---
With the Custom CSS Tool, Site Admins are able to write their own CSS to modify aspects of any template.

This tool is located within **Appearance > Custom CSS**.

For security purposes, all CSS is sanitized before being allowed onto the site. Once you hit update, you will notice that the formatting may change. That is the sanitizer [CSSTidy](http://csstidy.sourceforge.net/index.php) at work.

You can revert to the previous version of your custom CSS by clicking the **Revert to previous version** link that appears underneath the editor.

### Allowed CSS

The following CSS selectors, values, and properties will work in the Custom CSS plugin.

#### Default CSS

- [Default fields from HTML Purifier](http://htmlpurifier.org/live/smoketests/printDefinition.php)
  - Most of HTML4 and CSS2

#### Additional CSS

If your site needs to use CSS properties not listed here, look into [custom theming](http://aurora.uconn.edu/2016/03/24/themes-and-plugins/).

### Custom Block CSS

Sites using the Cynder theme and the assoicated block/Gutenberg editor can make use of custom CSS that is scoped to specific blocks. To do so, select a block, navigate to the block settings in the right sidebar, and click the Advanced dropdown menu. There you should see two options, one for additional CSS classes and another for just additional CSS.

![image-20260521-173236.png](media://3c90f4db-476a-4c39-8451-264dae7a8108)

- Additional CSS class(es) will apply the space-separated list of classes to the block, in case you want to apply CSS rules to specific blocks throughout the site.
- Additional CSS will apply actual CSS styling directly to the block itself, and will update the preview of the block you see in the editor. **While this can be useful, it’s recommended to use this approach sparingly, as it can be hard for site users/editors and network admins to trace problematic CSS to this setting.**