/// Determine a top/right/bottom/right value on a padding, margin, etc. property, no matter how many values were passed in. Use this function if you need to know the specific side of a value, but don't know if the value is using a shorthand format.
///
/// @param {List|Number} $val - Value to analyze. Should be a shorthand sizing property, e.g. "1em 2em 1em"
/// @param {Keyword} $side - Side to return. Should be `top`, `right`, `bottom`, or `left`.
///
/// @returns {Number} A single value based on `$val` and `$side`.
@function get-side($val, $side) {
    $length: length($val);

    @if $length == 1 {
        @return $val;
    }
    @if $length == 2 {
        @return map-get((
            top: nth($val, 1),
            bottom: nth($val, 1),
            left: nth($val, 2),
            right: nth($val, 2),
        ), $side);
    }
    @if $length == 3 {
        @return map-get((
            top: nth($val, 1),
            left: nth($val, 2),
            right: nth($val, 2),
            bottom: nth($val, 3),
        ), $side);
    }
    @if $length == 4 {
        @return map-get((
            top: nth($val, 1),
            right: nth($val, 2),
            bottom: nth($val, 3),
            left: nth($val, 4),
        ), $side);
    }
}