In Wave.video, you can zoom in and out of video or image.
In order to zoom in/out, head over to the step Edit and switch to the tab "Video/Image" (depending on whether you have a video or an image as your background).
You can zoom in and out of the video/image by clicking the corresponding + and - signs in the video editing section on the right.
The smart algorithm will automatically set a background of matching colors. However, you can always change the background color in the video editing section. Learn more about the video background here.