Brightness Slider

HTML

<div>
  <input type="range" id="opacity-slider" min=".4" max="1" step=".01" value="1">
  <p>
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  </p>
</div>

CSS

body {
  background-color: black;
  color: orange;
}

JavaScript

document.getElementById('opacity-slider').addEventListener('input', function (e) {
	document.body.style.opacity = this.value;
});