vendor/bower/bootstrap/less/mixins/nav-vertical-align.less

// Navbar vertical align
//
// Vertically center elements in the navbar.
// Example: an element has a height of 30px, so write out `.navbar-vertical-align(30px);` to calculate the appropriate top margin.
.navbar-vertical-align(@element-height) {
  margin-top: ((@navbar-height - @element-height) / 2);
  margin-bottom: ((@navbar-height - @element-height) / 2);
}