silverstripe-framework/admin/javascript/src/styles/_layout.scss

.cms-south-actions {  			// Todo: update variables
  height: 53px;					// navbar-total-height
  position: absolute;
  bottom: 0;
  width: 100%;
  border-top: 1px solid #ddd;	// $border-color
  background-color: #f6f7f8;	// $body-bg
  padding: 10px 15px; 			// $spacer-y*.625 $spacer-x
}