CSS (Cascading style sheets) control how elements of your website are displayed. With the correct knowledge, you could add custom CSS to change many parts of your website without editing your theme's code.
If you are unfamiliar with web development, read the theme manual to see if it's possible to make the style change using the theme's built in settings. Visit Locating theme manuals to locate information related to your theme.
- From your eCom admin, go to Design.
- On the right-hand side of the screen, select ADVANCED > Customize CSS.