Merge pull request #5067 from edx/gprice/forum-nav-header-width

Cosmetic fixes for forums

lms/static/sass/discussion/elements/_navigation.scss

@@ -17,6 +17,7 @@
   @include box-sizing(border-box);
   display: table;
   border-bottom: 1px solid $gray-l2;
+  width: 100%;
   background-color: $gray-l3;
 }
 

lms/static/sass/discussion/views/_thread.scss

@@ -32,6 +32,10 @@ body.discussion, .discussion-module {
       @extend %t-weight5;
     }
 
+    .posted-details .username {
+      font-size: inherit;
+    }
+
     .response-header-content {
       display: inline-block;
       vertical-align: top;