Scope css rules to the pipelines show page

Scope pipeline graph CSS rules could be moved a single file related to
the an individual pipeline page (projects:pipelines:show).

This change helps scope them only to that page while the rules are
moved.

app/assets/stylesheets/pages/pipelines.scss

@@ -386,19 +386,19 @@
       }
     }
   }
-}
 
-.pipeline-tab-content {
+  .pipeline-tab-content {
     display: flex;
     width: 100%;
     min-height: $dropdown-max-height-lg;
     background-color: $gray-light;
     padding: $gl-padding 0;
     overflow: auto;
-}
+  }
 
-// Pipeline graph
-.pipeline-graph {
+  // Pipeline graph, used at
+  // app/assets/javascripts/pipelines/components/graph/graph_component.vue
+  .pipeline-graph {
     white-space: nowrap;
     transition: max-height 0.3s, padding 0.3s;
 
@@ -642,15 +642,16 @@
       left: 1px;
       top: -2px;
     }
-}
+  }
 
-// Triggers the dropdown in the big pipeline graph
-.dropdown-counter-badge {
+  // Triggers the dropdown in the big pipeline graph
+  .dropdown-counter-badge {
     font-weight: 100;
     font-size: 15px;
     position: absolute;
     right: 13px;
     top: 8px;
+  }
 }
 
 .ci-build-text,