width and height doesn’t seem to work on :before pseudo-element

Note: The ::before and ::after pseudo-elements are actually laid display: inline; by default.

Change the display value to inline-block for the width & height to take effect while maintaining inline formatting context.

a.infolink::before {
    content: '?';
    display: inline-block;
    background: blue;
    color: white;
    width: 20px;
    height: 20px;
}

http://jsfiddle.net/C7rSa/3/