To give your post or page a sleek, professional look, you can add a Cover block.
Get started by clicking the + Inserter icon at the bottom-left corner of the screen and select the Cover block from the blocks list
It will look like this:
Once you insert the block, you have some options. You can either pick a background color by tapping on the color circles or you can insert a background media. If you select the option to Add Image or Video you will then need to select if where you would like to add the media from:
Once you select either a media or pick a color as your background you can also add text on top of it