/* Shared Components for all Subjects */

.back-btn {
    position: fixed;
    top: 2rem;
    left: 2rem;
    background: var(--text-main);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: 2rem;
    font-weight: 700;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    z-index: 3000;
    transition: var(--transition);
    border: none;
    text-decoration: none;
}

.back-btn:hover {
    transform: scale(1.05);
    background: var(--primary);
    box-shadow: var(--shadow);
}

.scroll-progress {
    position: fixed;
    top: 0;
    left: 0;
    height: 4px;
    z-index: 2500;
    width: 0%;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    transition: width 0.1s ease;
}

.app-container {
    display: grid;
    grid-template-columns: 320px 1fr;
    min-height: 100vh;
}

#sidebar {
    background: var(--surface);
    border-right: 1px solid var(--border);
    padding: 2.5rem 1.5rem;
    position: sticky;
    top: 0;
    height: 100vh;
    overflow-y: auto;
    z-index: 1000;
}

.logo {
    font-size: 1.6rem;
    font-weight: 800;
    color: var(--primary);
    margin-bottom: 3rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.nav-group {
    margin-bottom: 2.5rem;
}

.nav-label {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.15em;
    color: var(--text-muted);
    font-weight: 800;
    margin-bottom: 1.2rem;
    display: block;
    padding-left: 1rem;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    text-decoration: none;
    color: var(--text-muted);
    padding: 0.8rem 1rem;
    border-radius: 0.75rem;
    font-size: 0.9rem;
    font-weight: 600;
    margin-bottom: 0.3rem;
    transition: var(--transition);
}

.nav-item:hover {
    background: var(--bg);
    color: var(--primary);
    padding-left: 1.25rem;
}

.nav-item.active {
    background: var(--primary-light);
    color: var(--primary);
    box-shadow: var(--shadow);
}

#main-content {
    padding: 4rem 8% 8rem;
    max-width: 1300px;
    margin: 0 auto;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 5rem;
}

.mode-toggle {
    display: flex;
    background: var(--border);
    padding: 0.4rem;
    border-radius: 2rem;
    gap: 0.5rem;
}

.mode-btn {
    border: none;
    padding: 0.7rem 1.5rem;
    border-radius: 1.5rem;
    font-size: 0.9rem;
    font-weight: 700;
    cursor: pointer;
    transition: var(--transition);
    background: transparent;
    color: var(--text-muted);
}

.mode-btn.active {
    background: var(--surface);
    color: var(--primary);
    box-shadow: var(--shadow);
}

.unit-section {
    margin-bottom: 15rem;
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.6s ease-out;
}

.unit-section.visible {
    opacity: 1;
    transform: translateY(0);
}

.topic-badge {
    display: inline-block;
    background: var(--accent-2);
    color: #d68b4d;
    padding: 0.4rem 1.2rem;
    border-radius: 2rem;
    font-size: 0.8rem;
    font-weight: 800;
    margin-bottom: 1.5rem;
    text-transform: uppercase;
}

.topic-title {
    font-size: 3.5rem;
    line-height: 1.1;
    margin-bottom: 2rem;
    background: linear-gradient(135deg, var(--text-main) 0%, var(--primary) 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.intro-para {
    font-size: 1.25rem;
    color: var(--text-muted);
    max-width: 900px;
    margin-bottom: 4rem;
}

/* Concept Cards */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2rem;
    margin: 3rem 0;
}

.concept-card {
    background: var(--surface);
    border: 1px solid var(--border);
    padding: 2.5rem;
    border-radius: var(--radius);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.concept-card:hover {
    transform: translateY(-10px);
    border-color: var(--primary-light);
    box-shadow: var(--shadow);
}

.card-icon {
    font-size: 2.5rem;
    margin-bottom: 1.5rem;
    display: block;
}

/* Accordions */
.accordion {
    margin: 1.5rem 0;
    border-radius: var(--radius);
    overflow: hidden;
    border: 1px solid var(--border);
    background: var(--surface);
}

.acc-trigger {
    width: 100%;
    padding: 1.5rem 2rem;
    background: none;
    border: none;
    text-align: left;
    font-weight: 700;
    font-size: 1.15rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    transition: background 0.2s;
    color: var(--text-main);
}

.acc-trigger:hover {
    background: var(--bg);
}

.acc-content {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.accordion.open .acc-content {
    max-height: 2000px;
    padding: 0 2rem 2rem;
}

.acc-icon {
    transition: transform 0.3s ease;
}

.accordion.open .acc-icon {
    transform: rotate(180deg);
}

/* Tables */
.table-wrapper {
    overflow-x: auto;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    margin: 2.5rem 0;
    background: var(--surface);
}

table {
    width: 100%;
    border-collapse: collapse;
    text-align: left;
}

th {
    background: var(--primary-light);
    padding: 1.5rem;
    font-weight: 800;
    color: var(--primary);
    border-bottom: 2px solid var(--border);
}

td {
    padding: 1.25rem 1.5rem;
    border-bottom: 1px solid var(--border);
    vertical-align: top;
}

/* Callouts */
.callout {
    padding: 2.5rem;
    border-radius: var(--radius);
    margin: 4rem 0;
    display: flex;
    gap: 2rem;
    align-items: flex-start;
}

.callout.remember { background: #fff5eb; border: 1px solid #ffe3c9; }
.callout.exam { background: #f0f7ff; border: 1px solid #dbebff; }
.callout.tip { background: #ecfdf5; border: 1px solid #a7f3d0; }

/* Bookmark Feature UI */
.bookmark-btn {
    position: absolute;
    top: 1.5rem;
    right: 1.5rem;
    background: transparent;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    transition: var(--transition);
    opacity: 0.3;
}

.bookmark-btn.active {
    opacity: 1;
    color: #ffd700;
    transform: scale(1.2);
}

.bookmark-btn:hover {
    opacity: 1;
    transform: scale(1.1);
}

/* Quiz Mode UI */
.quiz-card {
    background: var(--surface);
    padding: 4rem;
    border-radius: 2rem;
    box-shadow: var(--shadow);
    max-width: 900px;
    margin: 0 auto;
    text-align: center;
    animation: fadeInUp 0.5s ease;
}

.opt-grid {
    display: grid;
    gap: 1rem;
    margin-top: 3rem;
}

.opt-btn {
    background: var(--bg);
    border: 2px solid var(--border);
    padding: 1.5rem;
    border-radius: 1rem;
    font-weight: 600;
    font-size: 1.1rem;
    cursor: pointer;
    transition: var(--transition);
    text-align: left;
    color: var(--text-main);
}

.opt-btn:hover {
    border-color: var(--primary);
    transform: translateX(5px);
}

.opt-btn.correct { background: var(--accent-3); border-color: #2ecc71; color: #155724; }
.opt-btn.wrong { background: var(--accent-1); border-color: #e74c3c; color: #721c24; }

@media (max-width: 1024px) {
    .app-container { grid-template-columns: 1fr; }
    #sidebar { display: none; }
    #main-content { padding: 2rem; }
    .topic-title { font-size: 2.5rem; }
}