Circles

Hi, I think this will be one of the easiest questions ever asked but here it goes…

im trying to draw a quarter circle 20 x 20 Pixels for a website as a corner. When it comes to drawing straight lines its fine, because there’s no curve they dont pixelate but i cant work out how to do a smooth and crisp corner.

The colours i am using is a grey (#999999) for ouside the line, Black as the line and red (#C60000) for inside the line.

Anybody got any tips that can help me?

Thanks, Chris