Page visuals allow you to choose different background images for different pages. You can also change the visual style of any widget. If you want to change workspace-level visuals, see this article.
Editing page visuals:
Open the "..." page menu in the top right corner of the page and click "edit page styles". Alternatively, you can find the same option in the "..." menu of any container or widget.
To edit the visuals of any element on the page, simply click on it while the visuals sidebar is open or select it from the dropdown menu. If you opened the sidebar from a container or widget menu, that container/widget is pre-selected.
You can edit page and container backgrounds, as well as change widget styles.
In the case of a heading widget, you can define the heading level for screen readers and otherwise edit it.
As you change visuals, you can see how it looks on the page in real time without having to close the sidebar or refresh the session.
When you're happy, click "save changes" at the bottom of the sidebar.