# Use custom CSS
Before you customize a theme, make a backup. Refer to Shopify help: Duplicating themes.
Our themes use a minified css file named
theme.min.css . This is a plain CSS file that's purged of unused styles, and it's minified to reduce the file's size. Using this file is the best option for most merchants, as our file optimizations can provide a slight performance boost.
However, you can continue to make your own changes and customizations. You can add your own CSS file, just for customizations, or use the unminified version of the file.
Add your own CSS file
If you don't need to change the existing CSS completely, but you want to override some of it or add your own CSS, continue using the minified file, and add your customizations into a new CSS file. The CSS from both files will be used together.
- Create a new CSS file.
- Point the theme to the new CSS file.
Create a new file named
custom.css in the
assets directory. If you plan to use Liquid inside this file, name the file
snippets/style-tags.liquid, point to your custom CSS file by inserting the following line at the end of the file:
This file is not minified. The file contains unused styles that might be useful for customizing the theme. For example, the file includes a complete set of grid system classes.