Is there a way to add a background color in a bar under the title and navigation in the OM template?

Hello!I'm currently using the OM template and I'd like to add a dark blue banner/bar across the top that works as a sort of background for the title, navigation bar, etc. Is there something I can edit or a code I can use to create that?

The temporary url for the site I'm working on is: https://hawk-corn-h4d2.squarespace.com

Thank you!

past this code in custom css box

.canvas-style-masthead-logo-left.header-subtitle-none #header, .canvas-style-masthead-logo-right.header-subtitle-none #header {
   padding-top: 0;
   background-color: blue; /* here you can add color code which you need*/
}

Yay! Thank you so much!

Is there a way I can make the bar taller and wider as well?