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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #0f172a;
    color: #e2e8f0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
}

.container {
    width: 100%;
    max-width: 800px;
    background: #1e293b;
    padding: 30px;
    border-radius: 16px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
}

header {
    text-align: center;
    margin-bottom: 25px;
}

header h1 {
    font-size: 1.8rem;
    color: #38bdf8;
    margin-bottom: 5px;
}

.breadcrumb {
    color: #94a3b8;
    font-size: 0.95rem;
}

.button-grid {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.menu-btn {
    background-color: #334155;
    color: #fff;
    border: 1px solid #475569;
    padding: 16px;
    font-size: 1.1rem;
    border-radius: 10px;
    cursor: pointer;
    text-align: left;
    transition: all 0.2s;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.menu-btn:hover {
    background-color: #0284c7;
    border-color: #0369a1;
}

.back-btn {
    background: transparent;
    border: none;
    color: #38bdf8;
    font-size: 1rem;
    cursor: pointer;
    padding: 5px 0;
    margin-bottom: 10px;
}

.back-btn:hover {
    text-decoration: underline;
}

.card {
    background: #334155;
    padding: 25px;
    border-radius: 12px;
}

.card h2 {
    color: #f43f5e;
    margin-bottom: 15px;
    font-size: 1.4rem;
}

#lectureText {
    line-height: 1.6;
    margin-bottom: 20px;
    font-size: 1.05rem;
}

.btn {
    background-color: #0284c7;
    color: white;
    border: none;
    padding: 12px 20px;
    font-size: 1rem;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.2s;
    width: 100%;
    margin-top: 15px;
}

.btn:hover {
    background-color: #0369a1;
}

.option-btn {
    display: block;
    width: 100%;
    padding: 12px;
    margin: 10px 0;
    background: #1e293b;
    border: 1px solid #475569;
    color: #fff;
    border-radius: 8px;
    text-align: left;
    cursor: pointer;
    transition: all 0.2s;
}

.option-btn:hover {
    background: #475569;
}

.option-btn.correct {
    background-color: #16a34a !important;
    border-color: #15803d;
}

.option-btn.wrong {
    background-color: #dc2626 !important;
    border-color: #b91c1c;
}

.hidden {
    display: none;
}

#resultText {
    margin-top: 15px;
    font-weight: bold;
    text-align: center;
}