I replaced an old wide base ceiling light with a new track lighting fixture. The new fixture is smaller and you can see unpainted ceiling and even the box behind it. I know there must be some kind of flat white metal plate that can cover the unsightly ceiling but i donít know what you call it, so i canít search for it on google or Amazon.

What do you call this flat covering?

How do i fix this?

Here is an image (i hope):
Name:  Light fixture too small IMG_1673.jpg
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