[p:first-child:first-letter not working in wordpress]

The URL is http://crispylogs.com/writing-high-quality-posts-to-increase-traffic-top-20-tips/

I am trying to add an effect, like a magazine's "drop-cap," but it's not working for me, and I don't know why.

The following is the CSS code I have used:

.single .entry p:first-child:first-letter {
float: left;
color: #903;
font-size: 47px;
line-height: 40px;
padding-top: 0px;
padding-right: 8px;
padding-left: 3px;
font-family: Georgia;
}