Help ME PLZ

I have tried to get the background image up for my page for hours now but not is working.
this:{background-image: url("https://picsart.com/i/image-344841446051201");}
is what ive been writing as well as some other things but nothing has worked so far. I've been using the website https://www.w3schools.com/css/css_background_image.asp but its not making sense. it you can please help me I would really appreciate it so much <3