// Calculate the total sum of a list
@function list-sum($list) {
  // zero out the initial sum
  $sum: 0;
  // loop through each value in the list adding it to $list-sum
  @for $i from 1 through length($list) {
    $sum: $sum + nth(nth($list, $i), 1);
  }
  @return nth($sum, 1);
}