Adding a css file to a custom theme I'm a very beginner in drupal and I just want to add a css file to my custom theme.

So I created a upjv.libraries.yml in themes/upjv and I added :

global-styling:
version: '8.4.4'
css:
   theme:
       css/styles-upjv.css: {}


And I have created a styles-upjv.css in themes/upjv/css. On my index page, my file isn't loaded and I don't know if it's because I created the file in a wrong place, if the content of my libraries.yml is correct. Can anyone help me on this little problem please ?
You have to add the following in your upjv.info.yml: 

libraries: 
  - upjv/global-styling


Make sure to clear cache after that by navigating to configuration &gt; Development &gt; Performance then clicking on Clear all caches under CLEAR CACHE.