update css properties and check for undefined size

Author: Alex Ford

tests/dummy/app/templates/scroll-position.hbs

@@ -20,10 +20,10 @@
   <hr />
 
 <div class="wrapper" style="box-sizing:border-box;">
-  <div class="simple-layout" style="float:left;width:40%;margin-top:-12px;margin-right:20px;">
+  <div class="simple-layout" style="float:left;width:40%;margin-top:-12px;padding-right:20px;">
     {{highlight-js code=markdown lang="javascript"}}
   </div>
-  <div class="simple-list" style={{{concat 'float:left;width:60px;position:relative;width:' containerWidth 'px;height:' containerHeight 'px;'}}}>
+  <div class="simple-list" style={{{concat 'float:left;width:60%;position:relative;width:' containerWidth 'px;height:' containerHeight 'px;'}}}>
     {{#ember-collection
        items=model
        estimated-height=containerHeight