/* ===========================
   Responsive Multi-Device CSS
   =========================== */

/* Body & Layout */
body {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: flex-start;
    align-items: center;
    margin: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: #495057;
}

.container-wrapper {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2rem;
    width: 90%;
    max-width: 1200px;
    margin: 2rem auto;
}

/* Header Section */
.header-section {
    background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
    color: white;
    padding: 2rem;
    text-align: center;
    margin-bottom: 2rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

/* Button Container */
.button-container {
    display: flex;
    gap: 20px;
    flex-wrap: wrap;
    justify-content: center;
    margin-bottom: 2rem;
}

.nav-button {
    background: white;
    color: #495057;
    text-decoration: none;
    padding: 1.5rem 2.5rem;
    border-radius: 15px;
    font-size: 1.2rem;
    font-weight: bold;
    text-align: center;
    min-width: 150px;
    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    border: 2px solid transparent;
    position: relative;
    overflow: hidden;
}

.nav-button:hover {
    transform: translateY(-6px);
    box-shadow: 0 12px 30px rgba(0, 0, 0, 0.3);
    background: #f8f9fa;
    border-color: #6c757d;
}

.nav-button:active {
    transform: translateY(-2px);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.nav-button i {
    display: block;
    margin-bottom: 10px;
    font-size: 2rem;
    color: #495057;
    transition: all 0.3s ease;
}

.nav-button:hover i {
    color: #667eea;
    transform: scale(1.1);
}

/* Subject Headers */
.subject-header {
    background: linear-gradient(90deg, #2c3e50, #34495e);
    color: white;
    padding: 1rem;
    margin: 2rem 0 1.5rem;
    border-radius: 8px;
    font-weight: bold;
    font-size: clamp(1.2rem, 2vw, 1.5rem);
}

/* Module Cards */
.module-card {
    border-left: 4px solid #3498db;
    margin-bottom: 1.5rem;
    padding-left: 1rem;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.module-card:hover {
    transform: translateX(5px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}
.module-title {
    font-weight: bold;
    color: #2c3e50;
    margin-bottom: 0.5rem;
    font-size: clamp(1rem, 1.5vw, 1.2rem);
}
.topic-list {
    list-style: none;
    padding-left: 0;
    margin-bottom: 0;
}
.topic-list li {
    padding: 0.3rem 0;
    border-bottom: 1px solid #ecf0f1;
    color: #34495e;
}
.topic-list li:last-child {
    border-bottom: none;
}
.page-number {
    color: #7f8c8d;
    font-size: 0.9rem;
}

/* TOC & Search */
.toc-container {
    background: white;
    border-radius: 10px;
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
.search-box {
    margin-bottom: 2rem;
}

/* Accordion */
.accordion-button {
    font-weight: 600;
    color: #2c3e50;
}
.accordion-button:not(.collapsed) {
    background-color: #3498db;
    color: white;
}

/* Footer */
.footer-section {
    background: #2c3e50;
    color: white;
    padding: 2rem 0;
    margin-top: 3rem;
    text-align: center;
}
.copyright-text {
    font-size: 0.9rem;
    color: #bdc3c7;
}

/* ===========================
   Responsive Media Queries
   =========================== */

/* Medium Devices <= 992px */
@media (max-width: 992px) {
    .container-wrapper {
        padding: 1.5rem;
    }
    .button-container {
        gap: 15px;
    }
    .nav-button {
        padding: 1.3rem 2rem;
        font-size: 1.1rem;
        min-width: 140px;
    }
    .nav-button i {
        font-size: 1.8rem;
        margin-bottom: 8px;
    }
}

/* Small Devices <= 768px */
@media (max-width: 768px) {
    .button-container {
        gap: 12px;
    }
    .nav-button {
        padding: 1.1rem 1.8rem;
        font-size: 1rem;
        min-width: 120px;
    }
    .subject-header {
        font-size: 1.2rem;
        padding: 0.8rem;
    }
    .nav-button i {
        font-size: 1.6rem;
    }
}

/* Extra Small Devices <= 480px */
@media (max-width: 480px) {
    .button-container {
        flex-direction: column;
        gap: 10px;
    }
    .nav-button {
        padding: 1rem 1.2rem;
        font-size: 0.95rem;
        min-width: 100%;
    }
    .nav-button i {
        font-size: 1.4rem;
    }
}