border-radius: 45px;
I love HTML5
You can use one value for all four corners.
border-radius: 90px / 50px;
I love CSS3
You can use two values to apply to the horizontal and vertical radius of every corner.
border-radius: border-radius: 50%;
I love JavaScript
You can use percentages.
border-radius: border-radius: 0px 0px 150px 150px;
I love jQuery
You can use four values, one for each corner.
border-radius:100% 100% 0% 100% / 100% 100% 0% 100%;
I love Photoshop
You can use eight values, one for horizontal/vertical radii of each corner.