UI: Repo header tweaks (#5945)

* UI: Repo header tweaks

- Use basic buttons on the header buttons, matching gogs
- Make 'Manage topic' text smaller, remove margin-left with no topics
present
- Move various inline styles to CSS
- Use flexbox on header title and buttons

* fix indentation

* reverse media query wrapping

* fix inconsisten whitespace

public/js/index.js

@@ -2605,7 +2605,7 @@ function initNavbarContentToggle() {
 function initTopicbar() {
     var mgrBtn = $("#manage_topic"),
         editDiv = $("#topic_edit"),
-        viewDiv = $("#repo-topic"),
+        viewDiv = $("#repo-topics"),
         saveBtn = $("#save_topic"),
         topicDropdown = $('#topic_edit .dropdown'),
         topicForm = $('#topic_edit.ui.form'),