Better styling for code review comment textarea (#11428)

* Better styling for code review comment textarea

* align tabular menu with textarea

* border around active tab instead of textarea

* border radius

* use .28571429rem

web_src/less/_review.less

@@ -66,12 +66,19 @@
         border: 0;
     }
 
-    .ui.attached.tabular.menu {
-        background: #f7f7f7;
+    .ui.active.tab {
         border: 1px solid #d4d4d5;
-        padding-top: 5px;
-        padding-left: 5px;
-        margin-top: 0;
+        padding: .5em;
+        border-radius: 0 .28571429rem .28571429rem .28571429rem;
+    }
+
+    .ui.active.markdown.tab {
+        border-top-left-radius: .28571429rem;
+    }
+
+    .ui.tabular.menu {
+        margin-bottom: 0;
+        border-bottom: 0;
     }
 
     .comment-list {