How to change content area width in blog post?

Themes
4

Hi, I’m having the same problem using EDITION theme.
I tried to modify the Header code under Settings > Code Injection > Site Header like this:

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.2.0/css/brands.min.css" integrity="sha512-+oRH6u1nDGSm3hH8poU85YFIVTdSnS2f+texdPGrURaJh8hzmhMiZrQth6l56P4ZQmxeZzd2DqVEMqQoJ8J89A==" crossorigin="anonymous" referrerpolicy="no-referrer" />

<style>
    .gh-head-menu .nav-twitter a {
        font-size: 0 !important;
    }

    .gh-head-menu .nav-twitter a::before {
        font-family: "Font Awesome 6 Brands";
        display: inline-block;
        font-size: 20px;
        font-style: normal;
        font-weight: normal;
        font-variant: normal;
        text-rendering: auto;
        -webkit-font-smoothing: antialiased;
    }

    .gh-head-menu .nav-twitter a::before {content: "\f099"}
    
 	@media (min-width: 992px) {
	  .col-lg-6 {
	    flex: 0 0 85% !important;
 	   max-width: 85% !important;
 	 }
	}
</style>

with no luck.

Note the @media part. I took that suggestion from https://forum.ghost.org/t/changing-post-width/29632

Can anyone help me out?