Use break-large css variable

src/static/stylesheets/content.scss

@@ -9,7 +9,7 @@
     color: $blue;
   }
   width: 100%;
-  @media (min-width: 992px) {
+  @media (min-width: $break-large) {
     width: 960px;
   }
 }

src/static/stylesheets/variables.scss

@@ -4,5 +4,4 @@ $white: #fdfdfd;
 $black: #2f2f2f;
 $blue: #144A98;
 $grey: #A9A9A9;
-$break-medium: 768px;
-$break-large: 1200px;
+$break-large: 992px;