$font_stack: 'Avenir Next W01', Helvetica, Arial, sans-serif;
$h1: 30px;
$h2: 26px;
$h3: 20px;
$h4: 16px;
$h5: 14px;
$h6: 12px;

$line-height-h1: 35px;
$line-height-h2: 35px;
$line-height-h3: 25px;
$line-height-h4: 25px;
$line-height-h5: 20px;
$line-height-h6: 20px;

$sizes: $h1 $h2 $h3 $h4 $h5 $h6;
$line_heights: $line-height-h1 $line-height-h2 $line-height-h3 $line-height-h4 $line-height-h5 $line-height-h6;

@mixin font-size($size) {
  font-size: nth($sizes, $size);
  line-height: nth($line_heights, $size);
}