The default Customizer tabs are enabled for any theme. However, some themes might remove these tabs and use custom tabs that have been generated by the theme. We have the ability to add custom tabs and settings to the customizer using Customizer API functions. The default settings available in the customizer are saved in the wp_options table of the WordPress database.

All the settings changes are temporary until we click the Publish button. The changes in the settings are previewed instantly in the site window on the right-hand side. The preview process is handled by enqueuing necessary details and styles with JavaScript. Since the changes are previewed instantly, many people will think the changes have been saved. However, you will lose the changes when refreshing the page if you don't click the Publish button.

Usually, we modify the settings and check how they are changed in the layout on the right-hand side. However, we have the option of clicking the Edit button icons on the right-hand side to load the respective settings for that section. The use of Edit buttons makes this process simpler. We should use the customizer to modify the content and check the existing theme, as well as check multiple themes without activating each theme on the site.