In the old days, we had to go to Photoshop (or some other image editor) to create rounded PNG or GIF files, to create images that were round. Now you can do this with simple CSS3 applied to your image:
This is what my picture looks like without the CSS:
This is just one small example, where CSS3 makes much of what we used to do with Photoshop in web design, obsolete. If you want to learn CSS3, my CSS course in my IWD package will teach you fast!