Adding custom CSS code to Joomla can be a useful way to customize the look and feel of your website. CSS (Cascading Style Sheets) is a style sheet language used to describe the presentation of a document written in a markup language like HTML. To start, you’ll need to create a CSS file and upload it to your Joomla website. Then, add the code to your template and apply it to your website. With a little bit of practice, you’ll be able to create beautiful and unique designs for your website.