Keep max width on MR content on side by side view

app/assets/stylesheets/pages/issuable.scss

@@ -1,3 +1,52 @@
+// Limit MR description for side-by-side diff view
+.fixed-width-container {
+  max-width: $limited-layout-width - ($gl-padding * 2);
+  margin-left: auto;
+  margin-right: auto;
+}
+
+.limit-container-width {
+  .detail-page-header {
+    @extend .fixed-width-container;
+  }
+
+  .issuable-details {
+    .detail-page-description,
+    .mr-source-target,
+    .mr-state-widget,
+    .merge-manually {
+      @extend .fixed-width-container;
+    }
+
+    .merge-request-tabs-holder {
+      &.affix {
+        border-bottom: 1px solid $border-color;
+
+        .nav-links {
+          border: 0;
+        }
+      }
+
+      .container-fluid {
+        @extend .fixed-width-container;
+      }
+    }
+  }
+
+  .merge-request-details {
+    .emoji-list-container {
+      @extend .fixed-width-container;
+    }
+  }
+
+  .diffs {
+    .mr-version-controls,
+    .files-changed {
+      @extend .fixed-width-container;
+    }
+  }
+}
+
 .issuable-details {
   section {
     .issuable-discussion {

app/views/projects/issues/show.html.haml

@@ -1,4 +1,4 @@
-- @content_class = "limit-container-width"
+- @content_class = "limit-container-width" unless fluid_layout
 - page_title           "#{@issue.title} (#{@issue.to_reference})", "Issues"
 - page_description     @issue.description
 - page_card_attributes @issue.card_attributes

app/views/projects/merge_requests/_show.html.haml

@@ -1,4 +1,4 @@
-- @content_class = "limit-container-width"
+- @content_class = "limit-container-width" unless fluid_layout
 - page_title           "#{@merge_request.title} (#{@merge_request.to_reference})", "Merge Requests"
 - page_description     @merge_request.description
 - page_card_attributes @merge_request.card_attributes
@@ -47,7 +47,7 @@
         = succeed '.' do
           = link_to "command line", "#modal_merge_info", class: "how_to_merge_link vlink", title: "How To Merge", "data-toggle" => "modal"
 
-    .content-block.content-block-small
+    .content-block.content-block-small.emoji-list-container
       = render 'award_emoji/awards_block', awardable: @merge_request, inline: true
 
     - if @commits_count.nonzero?