Bootstrap/docs/utilities/sizing-and-positioning.md

layout	title	group
docs	Sizing and positioning	utilities

Fixed positioning

The .pos-f-t class can be used to easily position elements at the top of the viewport and make them as wide as the viewport. Be sure you understand the ramifications of fixed-position elements within your project. Here's how the class is defined:

{% highlight scss %} .pos-f-t { position: fixed; top: 0; right: 0; left: 0; z-index: $zindex-navbar-fixed; } {% endhighlight %}

Full width

Easily make an element as wide as its parent using the .w-100 utility class, which sets width: 100%.

{% example html %} {% endexample %}