<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Dog Age Calculator</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <div class="calculator-container">
        <h1>Dog Age Calculator</h1>
        <p>Enter your dog's age in human years:</p>
        <input type="number" id="humanYears" placeholder="Enter human years" min="0">
        <button onclick="calculateDogAge()">Calculate</button>
        <p class="result" id="result"></p>
    </div>
    <script src="script.js"></script>
</body>
</html>

/* styles.css */

/* Reset */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Arial', sans-serif;
    background: linear-gradient(135deg, #ffafbd, #ffc3a0);
    color: #333;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
}

.calculator-container {
    background: #fff;
    padding: 20px 30px;
    border-radius: 10px;
    box-shadow: 0 8px 15px rgba(0, 0, 0, 0.2);
    text-align: center;
    width: 300px;
}

.calculator-container h1 {
    font-size: 24px;
    margin-bottom: 20px;
    color: #ff6f61;
}

.calculator-container input {
    width: 100%;
    padding: 10px;
    margin: 10px 0;
    border: 1px solid #ccc;
    border-radius: 5px;
    font-size: 16px;
}

.calculator-container button {
    background: #ff6f61;
    color: #fff;
    border: none;
    padding: 10px 15px;
    border-radius: 5px;
    font-size: 16px;
    cursor: pointer;
    transition: background 0.3s;
}

.calculator-container button:hover {
    background: #e55a4e;
}

.result {
    margin-top: 20px;
    font-size: 18px;
    color: #333;
    font-weight: bold;
}

// script.js

function calculateDogAge() {
    const humanYears = document.getElementById('humanYears').value;
    let dogYears;

    if (humanYears === "" || isNaN(humanYears) || humanYears <= 0) {
        dogYears = "Please enter a valid positive number!";
    } else if (humanYears <= 2) {
        dogYears = humanYears * 10.5;
    } else {
        dogYears = (2 * 10.5) + ((humanYears - 2) * 4);
    }

    document.getElementById('result').innerText = 
        typeof dogYears === "number"
        ? `Your dog's age in dog years is: ${dogYears.toFixed(1)}`
        : dogYears;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.