[doc] Make side fixed only for big screens

Also wrap the inline-toc in an accordion to
save some space.
Remove some of the unneeded javascript.

Fixes #4521

docs/css/customstyles.css

@@ -1007,9 +1007,9 @@ span.soft {
     }
 }
 
-@media (max-width: 990px) {
+@media (min-height: 600px) and (min-width: 990px) {
     #mysidebar {
-        position: relative;
+        position: fixed !important;
     }
 }
 
@@ -1025,6 +1025,15 @@ span.soft {
     }
 }
 
+#inline-toc-details {
+    display: none;
+}
+@media (max-width: 1350px) {
+    #inline-toc-details {
+        display: block;
+    }
+}
+
 .col-md-9 img {
     max-width: 100%;
     max-height: 100%;