.i_desk__item:last-child {
  /*width: -moz-calc(3rem + (100% - 4rem));
  width: calc(3rem + (100% - 4rem));*/
}

@media all and (min-width: 75em) {
  .i_desk__item:nth-last-child(-n+2) {
    width: -moz-calc(1rem + ((100% - 4rem) / 4 * 2));
    width: calc(1rem + ((100% - 4rem) / 4 * 2));
  }
}