Only limit container width on issues & MRs within fixed-width container

app/assets/stylesheets/pages/issuable.scss

 // Limit MR description for side-by-side diff view
-.limit-container-width {
-  .detail-page-header {
-    max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
-    margin-left: auto;
-    margin-right: auto;
-  }
-
-  .issuable-details {
-    .detail-page-description,
-    .mr-source-target,
-    .mr-state-widget,
-    .merge-manually {
+.container-limited {
+  &.limit-container-width {
+    .detail-page-header {
       max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
       margin-left: auto;
       margin-right: auto;
     }
 
-    .merge-request-tabs-holder {
-      &.affix {
-        border-bottom: 1px solid $border-color;
+    .issuable-details {
+      .detail-page-description,
+      .mr-source-target,
+      .mr-state-widget,
+      .merge-manually {
+        max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
+        margin-left: auto;
+        margin-right: auto;
+      }
+
+      .merge-request-tabs-holder {
+        &.affix {
+          border-bottom: 1px solid $border-color;
+
+          .nav-links {
+            border: 0;
+          }
+        }
 
-        .nav-links {
-          border: 0;
+        .container-fluid {
+          padding-left: 0;
+          padding-right: 0;
+          max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
+          margin-left: auto;
+          margin-right: auto;
         }
       }
+    }
 
-      .container-fluid {
-        padding-left: 0;
-        padding-right: 0;
+    .diffs {
+      .mr-version-controls,
+      .files-changed {
         max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
         margin-left: auto;
         margin-right: auto;
       }
     }
   }
-
-  .diffs {
-    .mr-version-controls,
-    .files-changed {
-      max-width: calc(#{$limited-layout-width} - (#{$gl-padding} * 2));
-      margin-left: auto;
-      margin-right: auto;
-    }
-  }
 }
 
 .issuable-details {