We can’t help you in this way
It is not possible to debug from a screenshot
You will need to post your code (both css and html) or a live version like on codepen
Code would make this so much easier to assist. However I did notice you are missing the end of your div tag on line 30.
Did you mean for that to be a
like @shadowfox476 says. Your ending
<div> tag is mistype.
Also, consider giving your div some width and height so you’ll know for sure that “background-color” is working.
Also try using [outline:2px dotted grey], it is handy for debugging css issues.
Thanks for help, I’ve solved my problem. Finally the background color is black :)).