To modify the background:
1. First, click to select a block.
2. Next, click Background in the left side panel.
3. Then, select a pattern or texture under Background Image. You can also change the Background Color (found above the patterns / textures) and decide on a color that complements your content!
You might find the background pattern or texture appears to not show (typically the grey ones under "background image"), but please note you must choose a color to activate any of these "grey' backgrounds so that the pattern shows "above" the chosen color. You can also adjust the opacity on either the color picker or on the actual background itself in our toolbar.
You can also add your own image as a background. Have experimenting with your backgrounds! :)