Issue 4460: Add CSS3 box-sizing property to Layout side panel

Steps to reproduce

  1. Inspect the blue <div> above
  2. Switch to the Layout side panel
  3. Have a look at the box-sizing value inside the Layout side panel
  4. Inspect the green <div> above
  5. Have a look at the box-sizing value inside the Layout side panel
  6. Inspect the yellow <div> above
  7. Have a look at the box-sizing value inside the Layout side panel

Expected Results