<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Responsive Form Layout</title>
    <style>
        body {
            font-family: Arial, sans-serif;
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            background-color: #f0f2f5;
        }
        .container {
            max-width: 800px;
            margin: 50px auto;
            padding: 20px;
            background-color: white;
            border-radius: 8px;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }
        .form-group {
            display: flex;
            flex-wrap: wrap;
            margin-bottom: 15px;
        }
        .form-group div {
            flex: 1;
            margin-right: 15px;
        }
        .form-group div:last-child {
            margin-right: 0;
        }
        .form-group label {
            display: block;
            margin-bottom: 5px;
            font-weight: bold;
        }
        .form-group input {
            width: 100%;
            padding: 10px;
            border: 1px solid #ddd;
            border-radius: 5px;
            font-size: 1em;
        }
        button {
            padding: 10px 20px;
            border: none;
            border-radius: 5px;
            background-color: #007bff;
            color: white;
            font-size: 1em;
            cursor: pointer;
        }
        button:hover {
            background-color: #0056b3;
        }
    </style>
</head>
<body>
    <div class="container">
        <h1>Responsive Form</h1>
        <form>
            <div class="form-group">
                <div>
                    <label for="firstName">First Name</label>
                    <input type="text" id="firstName">
                </div>
                <div>
                    <label for="lastName">Last Name</label>
                    <input type="text" id="lastName">
                </div>
            </div>
            <div class="form-group">
                <div>
                    <label for="email">Email</label>
                    <input type="email" id="email">
                </div>
                <div>
                    <label for="phone">Phone</label>
                    <input type="tel" id="phone">
                </div>
            </div>
            <button type="submit">Submit</button>
        </form>
    </div>
</body>
</html>