CSS (Cascading style sheets) determine how the elements of your website are displayed. With the right knowledge, you can add custom CSS to change many parts of your website without editing your theme's code.
If you're not familiar with web development, read the theme guide to see if it's possible to make the style change using the theme's built-in settings. Go to Finding Theme Tutorials for information related to your theme.
In other cases you can contact us. Our Support team is ready to help you and/or refer you to an external partner for making adjustments.
In your eCom admin, go to Design.
On the right side of the screen, select ADVANCED > Customize CSS.