Gallery Short code not working for my theme

Hi, I’m working with Roots theme, I found that the gallery short code is not working right with this theme. When I looked into the source code, the style sheet for gallery was not generated. I’m wondering what might cause this.

As I know from this post, the gellery short code should generate a style sheet like this:

<style type='text/css'>
 #gallery-1 {
     margin: auto;
}
 #gallery-1 .gallery-item {
     float: left;
     margin-top: 10px;
     text-align: center;
     width: 20%;
}
 #gallery-1 img {
     border: 2px solid #CFCFCF;
}
 #gallery-1 .gallery-caption {
     margin-left: 0;
 }
</style>

Here is the demo page of Roots theme, as you can see in the demo, gallery columns are not working as it should be. Anyone know how to fix this? I hope I can have the gallery code work as it is in Twenty Twelve theme.