CSS, Cascading Style Sheets, is a simple language made for customizing the look of your website - its fonts, background colors etc. CSS is present also in Prezi editor. If you're a beginner, you should use default options provided by Prezi. For more advanced users we recommend using built-in CSS editor.
Click on 'Customize' button on the top of the Prezi window and choose 'Advanced' on the right panel. In the window shown below click on 'Use the Prezi CSS editor'.
The @font-face setting allows you to modify three types of fonts in your Prezi presentation: title, subtitle and body. Below the main settings you can adjust those fonts in three different versions: bold, italic and bold+italic.
Next block of settings allows you to change your background. 'gradStart' and 'gradEnd' - initial and final gradient colors. You can add 'gradType: radial' parameter, If you want your gradient to go from the center to the outside.
Next block of settings allows you to adjust the colors of your fonts - title, subtitle and body. Color names are written in Hex Code. Learn more about it in this website.