curved css corners for some reason dont seem to work in IE9. I know it supports it however i have looked all over the web for a solution and cant find one that works for me. I tried putting <meta http-equiv="X-UA-Compatible" content="IE=9" /> but that did'nt work. I used the .htc file and behavior: url(border-radius.htc); however that only works sometimes when switching to compatibility mode. I even tried declairing all 4 values, and didnt make a diffrence. Work beautifuly in firefox, chrome, and safari but not in IE. Any help? Check it out: my web page If you have some debugging tool might help you help me.
Looks like the page is firing Quirks Mode, try moving those script & css includes down inside the tag... nothing should ever come between a doctype and it's html tag.
Detail explanation here Investigating Document Mode Issues
I found if your using the CSS style filter for IE8 and below browsers it will interfere with IE9 styles causing border-radius to not work and possible other ill effects.
To fix it add this to your html head:
<!--[if gte IE 9]>
<style type="text/css">.elementClass { filter: none !important; }</style>
<![endif]-->'
Use the vendor extensions, -moz-border-radius:15px; -ms-border-radius:15px; -o-border-radius:15px; -webkit-border-radius:15px; border-radius:15px;
You really only need the -ms version for what you want, but if you include them all you provide a broader spectrum of coverage.
I found that my border radius in ie9 is working on localhost but not on a server. Im using css3PIE to acomidate ie8 and below, would this be interfering with ie9?
IE9 don't need any prefix for border-radius (for sure you don't need -ms- prefix at least for this property!). Your browser probably have a problem. Maybe you're running beta or something like that.
Please test this demo in another IE9 running computer or have your IE restarted and try it to see IE9 renders border-radius just fine.
Quirks mode is where IE9 switches back to IE5 functionality (added following link to @seanmetzgar post also)
Detail explanation here Investigating Document Mode Issues
With a site I look after, which had ASP code right at the top of page, I added
<!DOCTYPE html>
just in front of the tag, below the code, and IE9 stopped going into Quirks Mode.
来源：https://stackoverflow.com/questions/7369796/ie9-border-radius