[FLINK-5742] [docs] allow sidenav to work for widths down to 992

This closes #3821

docs/_layouts/base.html

@@ -69,10 +69,10 @@ under the License.
       the _layouts directory goes here.
       {% endcomment %}
       <div class="row">
-        <div class="col-lg-3">
+        <div class="col-lg-3" id="sidenavcol">
           {% include sidenav.html %}
         </div>
-        <div class="col-lg-9 content">
+        <div class="col-lg-9 content" id="contentcol">
           {% if page.mathjax %}
           {% include latex_commands.html %}
           {% endif %}

docs/page/css/flink.css

@@ -30,6 +30,11 @@ body {
 	background: #f8f8f8;
 }
 
+@media (min-width: 992px) and (max-width: 1200px) {
+    #contentcol { float: left; width: 70%; }
+    #sidenavcol { float: left; width: 30%; }
+}
+
 /*=============================================================================
  Per page TOC
 =============================================================================*/