Out of the box, SXA sites have default styles for components, depending on your chosen grid and theme.
If you want to use custom grids or styles, you must configure them in the Content Editor, where you must build the structure of the site, including setting up the custom grid and configuring custom styles.
Learn more about configuring a custom SXA Horizon experience:
See reference material for elements that matter to the configuration:
After you have created a Horizon-compatible site, editors can edit it both in Horizon and in the Experience Editor. Therefore, we recommend that you test your configurations on both.