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Utilities

Bootstrap includes dozens of utilities—classes with a single purpose to reduce the frequency of highly repetitive declarations.

Sizing and positioning

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:

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

Width and height

Easily make an element as wide or as tall as its parent using the .w-100 and .h-100 utility classes.

Width = 100% 
<img class="w-100" src="..." alt="Width = 100%">
Full height
<div style="height: 100px; background-color: rgba(255,0,0,0.1);">
  <div class="h-100" style="width: 100px; background-color: rgba(0,0,255,0.1);">Full height</div>
</div>