_alexsmith1 on "Need help changing post title text for mobile visitors (CSS)"

I just recently purchased a new responsive theme. It has a separate section for mobile CSS (that hopefully functions correctly). Right now, the font size of the post titles is enormous (please visit a post from a mobile phone: example post).

I'd like to know what I can do in regards to CSS to fix this. I've done some searching around the forums already, someone said to use this code:

/** the post titles **/
h2.posttitle {
font-size: 14px;
}

but it didn't do anything.