Use the Backgrounds portion of the Theme settings to upload and assign high-quality images to portions of the theme.
Which images to use for backgrounds
Images used in these settings should be high-quality (large dimensions, high pixel density, etc.) JPGs. They should also lend well to repetition since the images will be repeated to fill the space.
Upload a 1920 x 1920px .JPG image here to display for the base background of the theme.
Upload a 1920 x 1920px .JPG image here to display for any feature using the Contrast style setting.
Upload a 1920 x 400px .JPG image here to display as the footer's background. This image can have a smaller height than the previous two settings since this is limited to the footer.