I am working on wordpress theme. Many websites and especially wordpress using rounded corners and I also want to use them, making my boxes look like this: http://illbequirky.com/. The problem is it doesn’t work in IE. Can anyone suggest me what should I do? 
border-radius works in IE now since version 9. Older browsers can just have square corners. If you really care, you can use JS for older browsers, such as http://css3pie.com/ .
Agree with @ralph_m; older browser don’t #need# rounded corners, they don’t change the content, and content is most important. you can’t make a website look exactly the same in every browser & operating system combination.
-webkit-border-radius:0.5em;
-moz-border-radius:0.5em;
-ms-border:radius:0.5em;
-o-border-radius:0.5em;
border-radius:0.5em;
Add those to whatever elements you need rounded. Change the value up or down for less or more roundness.
In most cases now you dont need the vendor prefixes, but for slightly older browsers it will help.