After creating a site, you can set the format of the site by applying a theme. This sets the colour and style of the header of each page in the site, and the colour of any sections that you apply emphasis to. You can also control the fonts of your site by choosing a dark or light variation on the theme.
To set the theme of your site:
Click on the Themes tab on the pane on the right-hand side of the screen
Click on the theme you wish to use
Under the theme name, choose the colour you wish to appl to the theme
Set a custom colour by clicking on the Custom drop-down and choosing a colour from the palette shown. You can also enter the 6 digit HEX code for a specific colour
Click on the Font Style drop-down arrow and choose the font variation you wish to use
All pages in the site will have the new theme applied - it is not possible to apply a theme to a single page only.