Position
.u-fixed
Applies fixed positioning on an element.
.u-fit
Sets position: absolute and sets top:0;right:0;bottom:0;left:0; (aka “trbl fitting”). Note that when using the fit attribute, there must be a container with fixed size and has position: relative layout. This is so the children know where to fit to.
.u-fullfill
It’s common to want the entire <body> to fit to the viewport. This class takes care of that.