Changing the background on profiles

How do I change the background in my profile?

I found everything myself

.UserCard.Hero.UserHero { 
width: 1070px; 
margin: 0 auto;
border-radius: 10px;
padding: 20px;
border: 1px solid Red;
}

I'm assuming this was related to the Profile Cover extension.

By default Flarum uses a background color based on the avatar's main color.