gistfile1.css

/* 
  Calculation to center diagonal separator:

  new width of the :before-element after the rotation (Pythagoras) = 25.46px
  add space to the right to visual center diagonal line: 25,46px / 2 = 12.73px
  total amount for A: 25.46px + 12.73px = 38.19px
  revise position of B: ( 25.46px - 18px ) / 2 = 3.73px; 

  change gap by adding half amount to B (+9px) than to A (+18px)
  slightly change for visual perfection
*/

.controls li, #main-nav li:first-child {
  padding: 0 0 0 56.19px; /* A */
}

.controls li:before, #main-nav li:first-child::before {
  position: absolute;
  display: inline-block;
  content: "";
  border-bottom: 1px solid #ddd;
  width: 18px;
  height: 18px;
  left: 12.73px; /* B */
  bottom: 9px;
  -webkit-transform: 	rotate(-45deg);
  -moz-transform: 	rotate(-45deg);
  -ms-transform: 		rotate(-45deg);
  -o-transform: 		rotate(-45deg);
  transform: 			rotate(-45deg);
}