Field containers don't seem to work for me

Field containers don't seem to work for me

I have a form you can see here which includes a label and an input inside a field container:

  1.     <div data-role="fieldcontain">
  2.         <label for="property_value">Property value</label>
  3.         <input type="number" name="property_value" id="property_value" value="" required />
  4.     </div>
 
Have I missed doing something else necessary to get the label and input to appear on the same line?
It seems to work okay in Firefox on a PC with a large screen, but on my Galaxy S3 I still see the label and input on separate lines and there is a thin line underneath them