Add Background styling applications

This should include the following:

**Customized CSS**
Setting the customized CSS styles as background. The Add Color button will set the color of the background, adding more than one color with the gradient set as Linear or Radial, the background image will be a gradient of the selected colors.

**Recommended CSS**
Code for searching for recommended CSS styles, from the colors used in the screenshot. Place the selected style as the background of the screenshot(s) in the gray space provided.

**Search an Suitable Image**
Search for the image when the input is entered to the search bar. The results will be in the form of rows of images that can be scrolled using a scrollbar on the right hand side. Place the selected image behind the screenshot(s) in the gray space provided.

**Upload Background Image**
An Upload button will open the device files pop-up, from which, any image can be selected. The selected image will then be set as the background of the screenshot(s).

Start by locating the screenshot area, gray background space, Add Color button, search bar, and Upload button described in the issue. Review the attached screenshots and existing background behavior first. Done means supporting custom gradients, recommended styles, searched images, and uploaded images as backgrounds for the screenshots.

Written by the indexing model from the issue text.