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Build a simple login system with CSS

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Code

/login-system
│
├── index.php         ← Login form
├── dashboard.php     ← Logged-in page
├── logout.php        ← Logout handler
├── users.txt         ← Stores user credentials
└── style.css         ← Optional: CSS styling

1. users.txt (sample users)
admin:admin123
rohan:pass456

2. index.php
php
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<?php
session_start();
$error = '';

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST['username'];
    $password = $_POST['password'];

    $lines = file('users.txt', FILE_IGNORE_NEW_LINES);
    foreach ($lines as $line) {
        list($user, $pass) = explode(':', trim($line));
        if ($user == $username && $pass == $password) {
            $_SESSION['username'] = $username;
            header("Location: dashboard.php");
            exit();
        }
    }
    $error = "Invalid username or password.";
}
?>

<!DOCTYPE html>
<html>
<head>
    <title>Login</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
<h2>Login</h2>
<form method="post" action="">
    <label>Username:</label><br>
    <input type="text" name="username" required><br><br>
    <label>Password:</label><br>
    <input type="password" name="password" required><br><br>
    <button type="submit">Login</button>
</form>
<p style="color:red;"><?php echo $error; ?></p>
</body>
</html>

3. dashboard.php

<?php
session_start();
if (!isset($_SESSION['username'])) {
    header("Location: index.php");
    exit();
}
?>

<!DOCTYPE html>
<html>
<head>
    <title>Dashboard</title>
</head>
<body>
<h2>Welcome, <?php echo $_SESSION['username']; ?>!</h2>
<p>This is your dashboard.</p>
<a href="logout.php">Logout</a>
</body>
</html>

4. logout.php

<?php
session_start();
session_destroy();
header("Location: index.php");
exit();

5. (Optional) style.css

body {
    font-family: Arial, sans-serif;
    margin: 50px;
}
input, button {
    padding: 8px;
    width: 200px;
}

Explanation

Here's a simple login system using HTML, CSS, and PHP with file-based user authentication (no database). This version is for educational/demo use only – real-world applications should use password hashing and database storage.

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