The code for this example above is actually quite simple:

<div style=" background-color: #ccc;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
border: 1px solid #000;
padding: 10px;" >

These different corners can also each be handled on their own, Mozilla has other names for the feature than the spec says it should have though, as it has f.i. -moz-border-radius-topright as opposed to -webkit-border-top-right-radius:
Mozilla/Firefox and Safari 3 users should see a box with a rounded left upper corner.

Mozilla/Firefox and Safari 3 users should see a box with a rounded right upper corner.

Mozilla/Firefox and Safari 3 users should see a box with a rounded left lower corner.

Mozilla/Firefox and Safari 3 users should see a box with a rounded right lower corner.

These are handled by / should be handled by:

    * -moz-border-radius-topleft / -webkit-border-top-left-radius
    * -moz-border-radius-topright / -webkit-border-top-right-radius
    * -moz-border-radius-bottomleft / -webkit-border-bottom-left-radius
    * -moz-border-radius-bottomright / -webkit-border-bottom-right-radius

http://www.css3.info/preview/rounded-border/

Css3 rounded corners

CSS3

CSS