Tremont Template: Make site/nav header background color expand full width of page

Site URL: https://akhusky.dog/

I'm currently using this, but the background color won't expand full-width (I tried assigning the width as 100%). I'm thinking it's the wrong class?

Thanks in advance.

.site-header {
  background-color: hsla(212, 100%, 27%, 0.3);

.site-header {
  	background-color: hsla(212, 100%, 27%, 0.3);
    margin: 0;
}