Sorry the previous post posted incorrectly at first. Thanks for your help!
I did that as well but it hasn’t changed. I’m in the process of moving a blog over from wordpress.com to siteground hosting and I haven’t pointed the nameservers over yet so I’m having to do all the changes using my hosts file on my local machine. This is causing some issues with wordpress and may be why I can’t resolve it at the moment.
I pasted the code into my style.css file under the theme folder that I am using but my header is still small. Do I need to paste it into a different style.css file?
Thanks