Twitter Bootstrap center elements

Question

I am looking for Twitter Bootstrap examples and do not understand how all elements in this example are centered? Using what tag or style?

Answer 1

It is because .container div is centered using auto margins.

.container {
 margin-right: auto;
 margin-left: auto;
}

Also .jumbotron has

text-align: center;

attribute which centers the the child 'Sign up' button.

Answer 2

Check out the helper classes in bootstrap here

Center content blocks Set an element to display: block and center via margin. Available as a mixin and class.

<div class="center-block">...</div>
 // Classes
 .center-block {
 display: block;
 margin-left: auto;
 margin-right: auto;
 }
 // Usage as mixins
.element {
 .center-block();
}