Apply better hierarchy to markdown headers and issue/mr titles

app/assets/stylesheets/framework/typography.scss

@@ -45,40 +45,38 @@
   }
 
   h1 {
-    font-size: 2em;
+    font-size: 1.75em;
     font-weight: 600;
-    margin: 1em 0 10px;
+    margin: 16px 0 10px;
     padding: 0 0 0.3em;
     border-bottom: 1px solid $btn-default-border;
     color: $gl-gray-dark;
   }
 
   h2 {
-    font-size: 1.6em;
+    font-size: 1.5em;
     font-weight: 600;
-    margin: 1em 0 10px;
-    padding-bottom: 0.3em;
-    border-bottom: 1px solid $btn-default-border;
+    margin: 16px 0 10px;
     color: $gl-gray-dark;
   }
 
   h3 {
-    margin: 1em 0 10px;
-    font-size: 1.4em;
+    margin: 16px 0 10px;
+    font-size: 1.3em;
   }
 
   h4 {
-    margin: 1em 0 10px;
-    font-size: 1.25em;
+    margin: 16px 0 10px;
+    font-size: 1.2em;
   }
 
   h5 {
-    margin: 1em 0 10px;
+    margin: 16px 0 10px;
     font-size: 1em;
   }
 
   h6 {
-    margin: 1em 0 10px;
+    margin: 16px 0 10px;
     font-size: 0.95em;
   }
 

app/assets/stylesheets/pages/detail_page.scss

@@ -20,9 +20,11 @@
 
 .detail-page-description {
   .title {
-    margin: 0;
-    font-size: 23px;
+    margin: 0 0 16px;
+    font-size: 2em;
     color: $gl-gray-dark;
+    padding: 0 0 0.3em;
+    border-bottom: 1px solid #e7e9ed;
   }
 
   .description {

app/assets/stylesheets/pages/merge_requests.scss

@@ -429,13 +429,6 @@
   }
 }
 
-.merge-request-details {
-
-  .title {
-    margin-bottom: 20px;
-  }
-}
-
 .merge-request-tabs {
   background-color: #fff;