Cursore gamma personalizzato con percentuale

https://www.w3schools.com/howto/tryit.asp?filename=tryhow_css_js_rangeslider

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.slidecontainer {
  width: 100%;
}

.slider {
  -webkit-appearance: none;
  width: 100%;
  height: 25px;
  background: #d3d3d3;
  outline: none;
  opacity: 0.7;
  -webkit-transition: .2s;
  transition: opacity .2s;
}

.slider:hover {
  opacity: 1;
}

.slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 25px;
  height: 25px;
  background: #4CAF50;
  cursor: pointer;
}

.slider::-moz-range-thumb {
  width: 25px;
  height: 25px;
  background: #4CAF50;
  cursor: pointer;
}
</style>
</head>
<body>

<h1>Custom Range Slider</h1>
<p>Drag the slider to display the current value.</p>

<div class="slidecontainer">
  <input type="range" min="1" max="100" value="50" class="slider" id="myRange">
  <p>Value: <span id="demo"></span></p>
</div>

slider.oninput = function() {
  output.innerHTML = this.value;
}
</script>

</body>
</html>

https://www.w3schools.com/howto/tryit.asp?filename=tryhow_css_js_rangeslider

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.slidecontainer {
width: 100%;
}

.slider {
-webkit-appearance: none;
width: 100%;
height: 25px;
background: #d3d3d3;
outline: none;
opacity: 0.7;
-webkit-transition: .2s;
transition: opacity .2s;
}

.slider:hover {
opacity: 1;
}

.slider::-webkit-slider-thumb {
-webkit-appearance: none;
appearance: none;
width: 25px;
height: 25px;
background: #4CAF50;
cursor: pointer;
}

.slider::-moz-range-thumb {
width: 25px;
height: 25px;
background: #4CAF50;
cursor: pointer;
}
</style>
</head>
<body>

<h1>Custom Range Slider</h1>
<p>Drag the slider to display the current value.</p>

<div class="slidecontainer">
<input type="range" min="1" max="100" value="50" class="slider" id="myRange">
<p>Value: <span id="demo"></span></p>
</div>

<script>
var slider = document.getElementById("myRange");
var output = document.getElementById("demo");
output.innerHTML = slider.value;

slider.oninput = function() {
output.innerHTML = this.value;
}
</script>

</body>
</html>