React Js Calculate Age by Date of Birth

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

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Age Calculator</title>
</head>

<body>
    <h2>Javascript Calculate date of birth (age) and Validation</h2>

<label for="dob">Enter Date of Birth:</label>
    <input type="date" id="dob" required>

<button onclick="calculateAge()">Calculate Age</button>

const today = new Date();
            const birthDate = new Date(dobInput.value);

if (birthDate > today) {
                resultElement.textContent = "Invalid date of birth. Please enter a valid date.";
                return;
            }

let ageInMilliseconds = today - birthDate;

// Calculate years
            const years = Math.floor(ageInMilliseconds / (365.25 * 24 * 60 * 60 * 1000));

// Calculate months
            const months = Math.floor((ageInMilliseconds % (365.25 * 24 * 60 * 60 * 1000)) / (30.44 * 24 * 60 * 60 * 1000));

// Calculate days
            const days = Math.floor((ageInMilliseconds % (30.44 * 24 * 60 * 60 * 1000)) / (24 * 60 * 60 * 1000));

resultElement.textContent = `Age: ${years} years, ${months} months, ${days} days`;
        }
    </script>
    <style>
        body {
            font-family: 'Arial', sans-serif;
            background-color: #f4f4f4;
            text-align: center;
            margin: 50px;
        }

h2 {
            color: #333;
        }

label {
            font-size: 18px;
            margin-top: 20px;
            display: block;
        }

input {
            padding: 12px;
            font-size: 16px;
            margin-bottom: 20px;
            border: 1px solid #ccc;
            border-radius: 4px;
            width: 200px
        }

button {
            background-color: #4caf50;
            color: white;
            padding: 12px 24px;
            font-size: 16px;
            cursor: pointer;
            border: none;
            border-radius: 4px;
        }

button:hover {
            background-color: #45a049;
        }

p {
            font-size: 20px;
            color: #333;
            margin-top: 20px;
            padding: 10px;
        }
    </style>
</body>

</html>