How to check if browser supports css3 rounded corners and svg

Basically i have web site where i want to check if client browser supports rounded corners and svg as well and if not i want to show the message that for best user experience is better to use the latest browser.

So how could i check for that?

UPDATE:

I just found such library called Modernizr, is it pos开发者_如何学JAVAsible to us that to check for that things?

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I'd recommend using Modernizr; I've found this the easiest way to detect features: Modernizr

On a side note, you can provide some CSS3 features to IE users by using CSS3 Pie. This includes an HTC file on the page that replicates these effects: CSS3 Pie