Move custom docs gutter to new class

site/assets/scss/_layout.scss

@@ -1,5 +1,8 @@
-.bd-layout {
+.bd-gutter {
   --bs-gutter-x: #{$bd-gutter-x};
+}
+
+.bd-layout {
 
   @include media-breakpoint-up(lg) {
     display: grid;

site/assets/scss/_masthead.scss

@@ -55,11 +55,6 @@
   padding: .8rem 2rem;
 }
 
-.bd-masthead-followup,
-.bd-masthead .container-xxl {
-  --bs-gutter-x: #{$bd-gutter-x};
-}
-
 .masthead-followup-icon {
   padding: 1rem;
   background-color: currentColor;

site/assets/scss/_navbar.scss

@@ -4,10 +4,6 @@
   background-image: linear-gradient(to bottom, rgba(var(--bd-violet-rgb), 1), rgba(var(--bd-violet-rgb), .95));
   box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .15), inset 0 -1px 0 rgba(0, 0, 0, .15);
 
-  .container-xxl {
-    --bs-gutter-x: #{$bd-gutter-x};
-  }
-
   .navbar-toggler {
     padding: 0;
     border: 0;