Add version control menu (#5222)

* Add version control menu

* Constify things

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Apply suggestions from code review

Co-authored-by: Julien Chaumond <chaumond@gmail.com>

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
Co-authored-by: Julien Chaumond <chaumond@gmail.com>

docs/source/_static/css/huggingface.css

@@ -1,5 +1,45 @@
 /* Our DOM objects */
 
+/* Version control */
+
+.version-button {
+    background-color: #6670FF;
+    color: white;
+    border: none;
+    padding: 5px;
+    font-size: 15px;
+    cursor: pointer;
+}
+
+.version-button:hover, .version-button:focus {
+    background-color: #A6B0FF;
+}
+ 
+.version-dropdown {
+    display: none;
+    background-color: #6670FF;
+    min-width: 160px;
+    overflow: auto;
+    font-size: 15px;
+}
+  
+.version-dropdown a {
+    color: white;
+    padding: 3px 4px;
+    text-decoration: none;
+    display: block;
+}
+  
+.version-dropdown a:hover {
+    background-color: #A6B0FF;
+}
+  
+.version-show {
+    display: block;
+}
+
+/* Framework selector */
+
 .framework-selector {
     display: flex;
     flex-direction: row;
@@ -38,6 +78,7 @@
 
 /* The research field on top of the toc tree */
 .wy-side-nav-search{
+    padding-top: 0;
     background-color: #6670FF;
 }