Fix comments header styles applying to comments

Previous way was a bad way of doing the styles and some of the rules
were leaking through into the comments themselves. This should be more
specific.

tildes/scss/modules/_topic.scss

@@ -245,23 +245,21 @@
   overflow: auto;
 }
 
-.topic-comments {
-  header {
-    display: flex;
-    flex-wrap: wrap;
-    align-items: center;
+.topic-comments-header {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
 
-    margin-bottom: 0.4rem;
+  margin-bottom: 0.4rem;
 
-    h2 {
-      margin-bottom: 0;
-      margin-right: 0.4rem;
-      white-space: nowrap;
-    }
+  h2 {
+    margin-bottom: 0;
+    margin-right: 0.4rem;
+    white-space: nowrap;
+  }
 
-    .form-listing-options {
-      margin-left: auto;
-    }
+  .form-listing-options {
+    margin-left: auto;
   }
 }
 

tildes/tildes/templates/topic.jinja2

@@ -144,7 +144,7 @@
 
 {% if topic.num_comments > 0 %}
   <section class="topic-comments">
-    <header>
+    <header class="topic-comments-header">
       <h2>
       {% trans num_comments=topic.num_comments %}
       {{ num_comments }} comment