modos/index.html

## index.html
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>HTML Color Test</title>
    <style type="text/css">
        #color_preview {
            width: 200px;
            height: 200px;
            border: 1px solid grey;
            background-color: white;
        }
    </style>
</head>

<body>
    <h1>HTML Color Test</h1>
    <input id="color_input" type="text" />
    <br /><br />
    <div id="color_preview"></div>
</body>

<script>
    let reg = /^([0-9a-f]{3}){1,2}$/i;
    let div = document.getElementById('color_preview');
    let input = document.getElementById('color_input');
    div.style.backgroundColor = 'black';

    input.addEventListener('input', (e) => {
        console.log(reg.test(input.value))
        if (reg.test(input.value)) {
            div.style.backgroundColor = '#' + input.value;
        } else {
            div.style.backgroundColor = 'black';
        }
    })
</script>

</html>
	<!DOCTYPE html>
	<html lang="en">

	<head>
	<meta charset="UTF-8">
	<title>HTML Color Test</title>
	<style type="text/css">
	#color_preview {
	width: 200px;
	height: 200px;
	border: 1px solid grey;
	background-color: white;
	}
	</style>
	</head>

	<body>
	<h1>HTML Color Test</h1>
	<input id="color_input" type="text" />
	<br /><br />
	<div id="color_preview"></div>
	</body>

	<script>
	let reg = /^([0-9a-f]{3}){1,2}$/i;
	let div = document.getElementById('color_preview');
	let input = document.getElementById('color_input');
	div.style.backgroundColor = 'black';

	input.addEventListener('input', (e) => {
	console.log(reg.test(input.value))
	if (reg.test(input.value)) {
	div.style.backgroundColor = '#' + input.value;
	} else {
	div.style.backgroundColor = 'black';
	}
	})
	</script>

	</html>