The theme editor lists the different variables which relate to the different customizable site elements, such as logo, navigation menu, footer, page background, etc.
While the variable list are grouped based on type and / or site and page major sections, the most convenient way to easily identify the element to target for customization is via the variable search utility, which is found at the top of the list of the left panel of the theme editor.
To use theme and style preset variable search utility:
Go to the Themes dashboard;
Hover over the target theme, and click the Edit button;
Click the search box at the top of the left pane of the theme editor;
Type the keywords that refers to the site elements that you would like to customize;
Click the group header to expand the variables that can be modified
Changes to any of the variables are automatically saved but not published. Once the variable change had been saved, the site previewer on the right of the theme editor are reloaded to preview the effect. Hit the Publish button to apply the variable change to the live site/s using the theme, or to make the change available for drafted site/s.