CSS and HTML updates to enable versioned core documentation (#28097)

* Updated header for versioned docs.

* A tree in a golden forest.

* Fixed spacing.

* Fixed CSS and text for previous version header.

docs/docsite/_themes/srtd/layout.html

@@ -155,14 +155,19 @@
     <nav data-toggle="wy-nav-shift" class="wy-nav-side">
 
       <div style="background-color:#5bbdbf;height=80px;margin:'auto auto auto auto'">
-        <a class="DocSiteProduct-header DocSiteProduct-header--core"
+        <a class="DocSiteProduct-header DocSiteProduct-header--core" href="http://docs.ansible.com">
-          href="http://docs.ansible.com/ansible/">
             <div class="DocSiteProduct-productName">
                 <div class="DocSiteProduct-logoText">
                     ANSIBLE  
+                    <div class="DocSiteProduct-CurrentVersion" align="right">
+                      v2.3
+                  </div>
                 </div>
             </div>
         </a>
+        
+
+          <div class="DocSiteProduct-CheckVersionPara">For previous versions, see the  <a class="DocSiteProduct-versionheader" href="http://docs.ansible.com/">documentation archive.</a></div> 
       </div>
 
       <div id="menu-id" class="wy-menu wy-menu-vertical" data-spy="affix">

docs/docsite/_themes/srtd/static/css/theme.css

@@ -4715,6 +4715,12 @@ span[id*='MathJax-Span'] {
     font-size: 20px;
 }
 
+.DocSiteProduct-CheckVersionPara {
+    padding-bottom: 20px;
+    margin-left: 10px;
+    margin-right: 10px;
+}
+
 .wy-menu-vertical a {
     padding: 0;
 }