HTML5 multiple range input

multiple-range-input.html

<!-- https://jsfiddle.net/z2ov274f/ -->
<div class="range" id="range">
  <input type="range" class="lower" min="0" max="10.5" value="5.0" step="0.5">
  <input type="range" class="upper" min="0" max="10.5" value="5.5" step="0.5">
</div>
<div id="lower-val"></div>
<div id="upper-val"></div>

multiple-range-input.js

var range = document.getElementById('range'),
  lower = range.querySelector('.lower'),
  upper = range.querySelector('.upper');

lower.onchange = upper.onchange = function() {
  if (lower === this) {
    var lowerValue = parseFloat(this.value), upperValue = parseFloat(upper.value);
    if (10.5 === lowerValue) {
      lowerValue = 10
      this.value = '10';
    }
    if (upperValue <= lowerValue) {
      upper.value = String(lowerValue + 0.5);
    }
  } else {
    var upperValue = parseFloat(this.value), lowerValue = parseFloat(lower.value);
    if (0.0 === upperValue) {
      upperValue = 0.5
      this.value = '0.5';
    }
    if (lowerValue >= upperValue) {
      lower.value = String(upperValue - 0.5);
    }
  }

  document.getElementById('lower-val').innerText = 'Lower: ' + lower.value;
  document.getElementById('upper-val').innerText = 'Upper: ' + upper.value;
};

multiple-range-input.scss

.range {
  position: relative;
  margin: 20px;
  height: 40px;
  border: 2px dashed lightgrey;
  background: white;
}

.range .lower,
.range .upper {
  position: absolute;
  top: 10px;
  width: 100%;
}

// https://github.com/darlanrod/input-range-scss/

$track-color: white !default;
$thumb-color: blue !default;

$thumb-radius: 0px !default;
$thumb-height: 20px !default;
$thumb-width: 20px !default;
$thumb-shadow-size: 0px !default;
$thumb-shadow-blur: 0px !default;
$thumb-shadow-color: rgba(0, 0, 0, 0) !default;
$thumb-border-width: 0px !default;
$thumb-border-color: white !default;

$track-width: 100% !default;
$track-height: 0px !default;
$track-shadow-size: 0px !default;
$track-shadow-blur: 1px !default;
$track-shadow-color: rgba(0, 0, 0, .0) !default;
$track-border-width: 0px !default;
$track-border-color: white !default;

$track-radius: 0px !default;
$contrast: 0% !default;

@mixin shadow($shadow-size, $shadow-blur, $shadow-color) {
  box-shadow: $shadow-size $shadow-size $shadow-blur $shadow-color, 0 0 $shadow-size lighten($shadow-color, 5%);
}

@mixin track {
  cursor: pointer;
  height: $track-height;
  transition: all .2s ease;
  width: $track-width;
}

@mixin thumb {
  @include shadow($thumb-shadow-size, $thumb-shadow-blur, $thumb-shadow-color);
  background: $thumb-color;
  border: $thumb-border-width solid $thumb-border-color;
  border-radius: $thumb-radius;
  cursor: pointer;
  height: $thumb-height;
  width: $thumb-width;
}

[type='range'] {
  -webkit-appearance: none;
  margin: $thumb-height / 2 0;
  width: $track-width;

  &:focus {
    outline: 0;

    &::-webkit-slider-runnable-track {
      background: lighten($track-color, $contrast);
    }

    &::-ms-fill-lower {
      background: $track-color;
    }

    &::-ms-fill-upper {
      background: lighten($track-color, $contrast);
    }
  }

  &::-webkit-slider-runnable-track {
    @include track;
    @include shadow($track-shadow-size, $track-shadow-blur, $track-shadow-color);
    background: $track-color;
    border: $track-border-width solid $track-border-color;
    border-radius: $track-radius;
  }

  &::-webkit-slider-thumb {
    @include thumb;
    -webkit-appearance: none;
    margin-top: ((-$track-border-width * 2 + $track-height) / 2) - ($thumb-height / 2);
  }

  &::-moz-range-track {
    @include track;
    @include shadow($track-shadow-size, $track-shadow-blur, $track-shadow-color);
    background: $track-color;
    border: $track-border-width solid $track-border-color;
    border-radius: $track-radius;
  }

  &::-moz-range-thumb {
    @include thumb;
  }

  &::-ms-track {
    @include track;
    background: transparent;
    border-color: transparent;
    border-width: ($thumb-height / 2) 0;
    color: transparent;
  }

  &::-ms-fill-lower {
    @include shadow($track-shadow-size, $track-shadow-blur, $track-shadow-color);
    background: darken($track-color, $contrast);
    border: $track-border-width solid $track-border-color;
    border-radius: $track-radius * 2;
  }

  &::-ms-fill-upper {
    @include shadow($track-shadow-size, $track-shadow-blur, $track-shadow-color);
    background: $track-color;
    border: $track-border-width solid $track-border-color;
    border-radius: $track-radius * 2;
  }

  &::-ms-thumb {
    @include thumb;
    margin-top: 0;
  }
}