How Can You Center A Gallery With Html And Css

I am quit new to html and css and hope someone can help. With help of w3 schools (http://www.w3schools.com/CSS/css_image_gallery.asp) I created an simple gallery. With this the

Solution 1:

Wrap everything in a div with an id of container. Then add #container { width: 100px; margin: 0 auto; replacing 100px with how wide you want the gallery to be.