Header CSS

I am currently working on a site for a client and I am having a few issues changing the header background colour.

By using the developer tools in Google Chrome, I am able to change the background as needed however, when I then add this into my Style sheet, it doesn’t work.

Basically, I need to set the header-body background to a specific colour. I tried adding below to my style sheet,

.header-body {
background: #f2f2f2;
}

that didn’t work, I also tried adding !important to it and no changes.

Could someone please assist that would be grand!