* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    min-height: 100vh;
    padding: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
}

.container {
    background: white;
    border-radius: 15px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    padding: 30px;
    width: 100%;
    max-width: 600px;
    text-align: center;
}

h1 {
    color: #2c3e50;
    margin-bottom: 20px;
    font-size: 28px;
}

.course-card {
    background: #f8f9fa;
    border-radius: 10px;
    padding: 20px;
    margin: 20px 0;
    transition: transform 0.3s, box-shadow 0.3s;
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
}

.course-card h2 {
    color: #3498db;
    margin-bottom: 10px;
}

.btn {
    background: #3498db;
    color: white;
    border: none;
    border-radius: 50px;
    padding: 12px 25px;
    font-size: 16px;
    cursor: pointer;
    margin: 10px 5px;
    transition: background 0.3s, transform 0.2s;
}

.btn:hover {
    background: #2980b9;
    transform: scale(1.05);
}

.control-panel {
    background: #f1f2f6;
    padding: 20px;
    border-radius: 10px;
    margin: 25px 0;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    align-items: center;
    gap: 15px;
}

.control-panel input[type="range"] {
    width: 200px;
}

.status {
    background: #e8f4fc;
    padding: 15px;
    border-radius: 10px;
    margin-top: 20px;
    text-align: left;
}

.status p {
    margin: 8px 0;
    font-size: 16px;
}

.status span {
    font-weight: bold;
    color: #e74c3c;
}

.password-input {
    display: flex;
    justify-content: center;
    margin: 20px 0;
}

.password-input input {
    padding: 12px 15px;
    border: 2px solid #3498db;
    border-radius: 50px 0 0 50px;
    width: 70%;
    font-size: 16px;
    outline: none;
}

.password-input button {
    border-radius: 0 50px 50px 0;
    margin-left: -2px;
}

.error {
    color: #e74c3c;
    margin-top: 10px;
    min-height: 20px;
}

.hidden {
    display: none;
}

.footer {
    margin-top: 30px;
    color: #7f8c8d;
    font-size: 14px;
}