How to Make a Gradient Background in WordPressby Sara Williams
Cascading Style Sheet Web design code includes a gradient option, so you can add CSS-only gradient backgrounds to your WordPress websites without any need for sliced images. In WordPress, you cannot apply the gradient to the body tag as you would for solid backgrounds, but you can use a div container that wraps around the entire website. Many themes built on CSS frameworks already include such a div, though you can add one if your theme does not.
Go to the wp-admin directory of your website and log in to the WordPress dashboard. Navigate to Appearance and click the Editor link. Click the link to header.php under the Templates heading to load the HTML file containing your website's body tag.
Look for a div with an ID of "container" directly below the body tag in your header.php file. If you do not find one, add one. Here is what it should look like: