In a fixed width layout it is simple to specify both the width and the height of an element, but what we want in this example, is to specify the with and height of an element as percentages, that are related btween them, and not the container.
The normal way of delivering iconography on websites was traditionally the use of bitmap formats such as PNG. They're quick and direct, and they ensure out final results.
The use of web fonts have given us another alternative. By definition, they're scalable and resolution-independent. No need to specify higher resolution graphics for high resolution screens.
Lets see some examples: