You can add an image, a video or a color to the site’s background.
For that click on the block settings:
In the new window navigate to the Background tab, then choose one of the three options - Color, Image, Video.
Color - allows you to add a solid color or gradient. To choose a color, hover over and click on the Custom color icon. Adjust the opacity with the toggle to the right of the palette:
Image - here you can upload your own image or choose one of the existing ones by clicking on the Gallery:
By clicking on Gallery, you’ll have an option to add one of the images already on the site, or a free photo:
When you add an image, additional settings will become available to you - scroll effects, color overlay, filters, color behind image:
In the Video section you can add a link to a video from Youtube or Vimeo:
After the video is added, you can go ahead and adjust the color overlay to match it to the site colors: