:root {
    --bg-color: #f4f6f8;
    --text-color: #333;
    --card-bg: #ffffff;
    --input-bg: #ffffff;
    --input-text: #000000;
    --border-color: #ccc;
    --btn-bg: #007bff;
    --btn-hover: #0056b3;
    --btn-text: #ffffff;
    --shadow-color: rgba(0,0,0,0.1);
    --icon-color: #333;
}
[data-theme="dark"] {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --card-bg: #1e1e1e;
    --input-bg: #2c2c2c;
    --input-text: #e0e0e0;
    --border-color: #444;
    --btn-bg: #0d6efd;
    --btn-hover: #0b5ed7;
    --btn-text: #ffffff;
    --shadow-color: rgba(0,0,0,0.5);
    --icon-color: #e0e0e0;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 20px;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    transition: background-color 0.3s, color 0.3s;
}

form {
    background: var(--card-bg);
    padding: 40px;
    border-radius: 10px;
    box-shadow: 0 10px 25px var(--shadow-color);
    width: 100%;
    max-width: 400px;
    position: relative;
    text-align: center;
    transition: background-color 0.3s, box-shadow 0.3s;
}

h2 { margin-top: 0; margin-bottom: 20px; color: var(--text-color); }

input {
    width: 100%;
    padding: 12px;
    margin: 10px 0;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    box-sizing: border-box;
    background-color: var(--input-bg);
    color: var(--input-text);
    font-size: 1em;
}

button[type="submit"] {
    width: 100%;
    padding: 12px;
    background: var(--btn-bg);
    color: var(--btn-text);
    border: none;
    border-radius: 5px;
    font-weight: bold;
    cursor: pointer;
    font-size: 1em;
    margin-top: 10px;
    transition: background 0.2s;
}
button[type="submit"]:hover { background: var(--btn-hover); }

.error { color: #dc3545; margin-bottom: 15px; font-size: 0.9em; }

#themeToggle {
    position: absolute;
    top: 15px;
    right: 15px;
    background: transparent;
    border: none;
    font-size: 1.5em;
    cursor: pointer;
    color: var(--icon-color);
    padding: 5px;
    border-radius: 50%;
    transition: background 0.2s;
}
#themeToggle:hover { background: rgba(0,0,0,0.1); }
[data-theme="dark"] #themeToggle:hover { background: rgba(255,255,255,0.1); }