Format a heading in Twenty Eleven child theme

Hi,
I’m trying to change the way my h4 heading is displayed, but no matter what I do in child theme style.css – it gets overwritten by original style.css.

Originaly I tried this:

h4 {
color: red;
}

then

.entry-content h4 {
color: red;
}

but nothing happens.
I’ve watched and read a bunch of tutorials online about selectors, but still can’t get it to work.
What am I doing wrong?

Here’s the link, I’m trying to format gallery headings.