A theme defines the look and feel of websites in Veva. All pages in a Veva website belong to a certain template, which in turn belongs to a certain theme. You can have multiple Themes installed at the same time and use them all at once, i.e. one page can use Theme A while another page can use Theme B.

If your theme is responsive (uses CSS media-queries), it should expose those media-query breakpoints so the Veva page editor knows about them. Veva will then display buttons for each breakpoint above the page editor, so the user can view (and edit) the pages in all the different device widths that the theme supports.

Many content components in Veva allow the user to change their styling by selecting CSS classes to apply to them. This CSS class selector lists all CSS classes which the theme provides.

You might want the user to be able to change some aspects of your theme, without using the page/template editor to actually edit content. Let's say that your theme had a header with the name of the company and a logo.