move styling from js to css

IPython/html/static/notebook/js/pager.js

@@ -75,9 +75,7 @@ define([
     };
 
     Pager.prototype.style = function () {
-        this.pager_splitter_element.addClass('border-box-sizing ui-widget ui-state-default');
-        this.pager_element.addClass('border-box-sizing');
-        this.pager_element.find(".container").addClass('border-box-sizing');
+        this.pager_splitter_element.addClass('ui-widget ui-state-default');
         this.pager_splitter_element.attr('title', 'Click to Show/Hide pager area, drag to Resize');
     };
 

IPython/html/static/notebook/less/pager.less

@@ -1,10 +1,12 @@
 div#pager_splitter {
     height: 8px;
+    .border-box-sizing();
 }
 
 #pager-container {
     position: relative;
     padding: 15px 0px;
+    .border-box-sizing();
 }
 
 div#pager {
@@ -19,4 +21,5 @@ div#pager {
       background-color: @cell_background;
       padding: @code_padding;
     }
+    .border-box-sizing();
 }