Fix empty running table background

* Add list_placeholder style
* Change id so list_header class doesn't get added by JS

IPython/html/static/style/style.min.css

@@ -8665,6 +8665,13 b' ul.breadcrumb span {'
   font-weight: bold;
   background-color: #eeeeee;
 }
+.list_placeholder {
+  font-weight: bold;
+  padding-top: 4px;
+  padding-bottom: 4px;
+  padding-left: 7px;
+  padding-right: 7px;
+}
 .list_container {
   margin-top: 4px;
   margin-bottom: 20px;

IPython/html/static/tree/js/kernellist.js

@@ -49,7 +49,7 b' define(['
                 type: 'notebook',
             }, item);
         }
-        $('#running_list_header').toggle($.isEmptyObject(d));
+        $('#running_list_placeholder').toggle($.isEmptyObject(d));
     };
 
     KernelList.prototype.add_link = function (model, item) {

IPython/html/static/tree/less/tree.less

@@ -62,6 +62,14 b' ul.breadcrumb {'
     background-color: @page-backdrop-color
 }
 
+.list_placeholder {
+    font-weight: bold;
+    padding-top: @dashboard_tb_pad;
+    padding-bottom: @dashboard_tb_pad;
+    padding-left: @dashboard_lr_pad;
+    padding-right: @dashboard_lr_pad;
+}
+
 .list_container {
   margin-top: @dashboard_tb_pad;
   margin-bottom: 5*@dashboard_tb_pad;

IPython/html/templates/tree.html

@@ -123,7 +123,7 b' data-terminals-available="{{terminals_available}}"'
               <div id="collapseOne" class=" collapse in">
                 <div class="panel-body">
                   <div id="terminal_list">
-                    <div id="terminal_list_header" class="row list_header">
+                    <div id="terminal_list_header" class="row list_placeholder">
                     {% if terminals_available %}
                       <div> There are no terminals running. </div>
                     {% else %}
@@ -143,7 +143,7 b' data-terminals-available="{{terminals_available}}"'
               <div id="collapseTwo" class=" collapse in">
                 <div class="panel-body">
                   <div id="running_list">
-                    <div id="running_list_header" class="row list_header">
+                    <div id="running_list_placeholder" class="row list_placeholder">
                       <div> There are no notebooks running. </div>
                     </div>
                   </div>