Welcome to the first of a series of "quick tips" I'll be doing.
The first one starts with a fun technique for rounded corners (without images) on your webpage.
In your HTML you will need a div such as:
<div class="rounded"><p>Example div</p></div>
And then in your CSS we will style that box by giving it a width, height, background-color and then applying the browser specific border-radius properties.
#rounded { width:150px; height:150px; background-color:grey; border-radius:8px; -moz-border-radius:8px; -webkit-border-radius:8px;}
The first border-radius property will give us rounded corners in the Opera browser.
The second -moz-border-radius property is for Gecko based browsers (like Mozilla Firefox).
The third and final property -webkit-border-radius is for WebKit based browsers like Google Chrome and Apple's Safari.
For more information about CSS3, I recommend CSS3.info.
Enjoy!