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

html {
    scroll-behavior: smooth;
}

:root {
    --accent: #2F8F7A;
    --accent-dark: #20624F;
    --radius: 14px;
}

body {
    font-family: 'Vazirmatn', sans-serif;
    color: var(--ink);
    background-color: var(--paper);
    background-image:
        linear-gradient(var(--grid) 1px, transparent 1px),
        linear-gradient(90deg, var(--grid) 1px, transparent 1px);
    background-size: 26px 26px;
    min-height: 100vh;
    line-height: 1.7;
    transition: background-color 0.2s, color 0.2s;
}

a {
    color: inherit;
    text-decoration: none;
}

button {
    font-family: inherit;
    cursor: pointer;
}

.display {
    font-family: 'Lalezar', sans-serif;
    letter-spacing: 0.5px;
}

.mono {
    font-family: 'JetBrains Mono', monospace;
}

:focus-visible {
    outline: 3px solid var(--red);
    outline-offset: 3px;
    border-radius: 4px;
}

@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        transition-duration: 0.01ms !important;
    }
}

.wrap {
    max-width: 1120px;
    margin: 0 auto;
    padding: 0 24px;
}

header {
    position: sticky;
    top: 0;
    z-index: 50;
    background: color-mix(in srgb, var(--paper) 90%, transparent);
    backdrop-filter: blur(6px);
    border-bottom: 2px dashed var(--grid);
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 14px 24px;
    gap: 14px;
    flex-wrap: wrap;
}

.brand {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 1.4rem;
    font-family: 'Lalezar', sans-serif;
}

.brand-logo {
    height: 36px;
    width: auto;
    flex: none;
}

.brand span {
    color: var(--red);
}

.nav-actions {
    display: flex;
    align-items: center;
    gap: 14px;
}

.home-link {
    font-size: 0.9rem;
    color: var(--ink-soft);
    font-weight: 600;
}

.theme-toggle {
    border: 1px solid var(--card-border);
    background: var(--panel-bg);
    color: var(--ink);
    border-radius: 999px;
    padding: 8px 16px;
    font-size: 0.85rem;
    font-weight: 600;
}

.hero {
    padding: 60px 0 40px;
    text-align: center;
}

.hero h1 {
    font-size: clamp(2.1rem, 5vw, 3.4rem);
    line-height: 1.25;
    margin-bottom: 16px;
}

.hero h1 em {
    font-style: normal;
    color: var(--red);
}

.hero p {
    color: var(--ink-soft);
    font-size: 1.02rem;
    max-width: 520px;
    margin: 0 auto;
}

.underline-mark {
    display: block;
    width: 180px;
    height: 10px;
    margin: 14px auto 0;
    background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 180 10'%3E%3Cpath d='M2 7 C40 2, 80 9, 120 4 S170 8, 178 3' fill='none' stroke='%23D0473C' stroke-width='3' stroke-linecap='round'/%3E%3C/svg%3E") no-repeat center / contain;
}

.covers {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 28px;
    padding: 20px 0 72px;
}

@media (max-width: 820px) {
    .covers {
        grid-template-columns: 1fr;
        max-width: 360px;
        margin: 0 auto;
    }
}

.cover {
    appearance: none;
    border: none;
    text-align: right;
    color: #fff;
    border-radius: var(--radius);
    padding: 28px 22px 22px;
    min-height: 250px;
    position: relative;
    overflow: hidden;
    box-shadow: 0 10px 30px -12px var(--shadow-color);
    transition: transform 0.25s ease;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    gap: 10px;
}

.cover:hover,
.cover:focus-visible {
    transform: translateY(-6px) rotate(-0.4deg);
}

.cover::before {
    content: "";
    position: absolute;
    top: 0;
    right: 20px;
    left: 20px;
    height: 22px;
    background-image: radial-gradient(circle, var(--paper) 0 5px, transparent 5.5px);
    background-size: 26px 100%;
    background-repeat: repeat-x;
    opacity: 0.9;
}

.cover .num {
    font-family: 'Lalezar', sans-serif;
    font-size: 4rem;
    line-height: 1;
    opacity: 0.92;
    align-self: flex-start;
}

.cover .label {
    font-size: 1.12rem;
    font-weight: 700;
}

.cover .sub {
    font-size: 0.83rem;
    opacity: 0.85;
}

.cover .go {
    margin-top: 8px;
    align-self: flex-start;
    font-size: 0.83rem;
    font-weight: 600;
    border-bottom: 2px solid rgba(255, 255, 255, 0.65);
    padding-bottom: 2px;
}

.features {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 16px;
    padding: 0 0 80px;
}

@media (max-width: 900px) {
    .features {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .features {
        grid-template-columns: 1fr;
    }
}

.feature {
    background: var(--paper-2);
    border-radius: 10px;
    padding: 18px 16px;
    border: 1px solid var(--card-border);
}

.feature svg {
    width: 26px;
    height: 26px;
    color: var(--red);
    margin-bottom: 10px;
}

.feature h3 {
    font-size: 0.95rem;
    margin-bottom: 4px;
}

.feature p {
    font-size: 0.8rem;
    color: var(--ink-soft);
}

.grade-head {
    display: flex;
    align-items: center;
    gap: 16px;
    margin: 30px 0 26px;
    flex-wrap: wrap;
}

.grade-head .chip {
    font-family: 'Lalezar', sans-serif;
    font-size: 1.7rem;
    color: #fff;
    width: 54px;
    height: 54px;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex: none;
    background: linear-gradient(160deg, var(--accent), var(--accent-dark));
}

.grade-head h2 {
    font-size: 1.5rem;
}

.grade-head p {
    color: var(--ink-soft);
    font-size: 0.88rem;
}

.tabs-layout {
    display: flex;
    gap: 22px;
    align-items: flex-start;
    padding-bottom: 60px;
}

@media (max-width: 760px) {
    .tabs-layout {
        flex-direction: column;
    }
}

.tabs {
    display: flex;
    flex-direction: column;
    gap: 8px;
    flex: 0 0 210px;
}

@media (max-width: 760px) {
    .tabs {
        flex-direction: row;
        flex-wrap: wrap;
        flex: none;
        width: 100%;
    }
}

.tab-btn {
    display: flex;
    align-items: center;
    gap: 10px;
    background: var(--paper-2);
    border: 1px solid var(--card-border);
    border-radius: 10px;
    padding: 12px 14px;
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--ink-soft);
    text-align: right;
    transition: transform 0.15s, background 0.2s, color 0.2s;
}

@media (max-width: 760px) {
    .tab-btn {
        flex: 1 1 150px;
    }
}

.tab-btn svg {
    width: 18px;
    height: 18px;
    flex: none;
}

.tab-btn:hover {
    transform: translateX(-4px);
}

@media (max-width: 760px) {
    .tab-btn:hover {
        transform: translateY(-2px);
    }
}

.tab-btn.active {
    background: var(--accent);
    color: #fff;
    box-shadow: 0 10px 24px -10px var(--shadow-color);
}

#content-frame {
    flex: 1;
    width: 100%;
    min-height: 70vh;
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    background: var(--panel-bg);
    box-shadow: 0 10px 30px -14px var(--shadow-color);
}

.content-page {
    padding: 34px 0 60px;
}

.back-bar {
    margin-bottom: 22px;
}

.breadcrumb {
    font-size: 0.82rem;
    color: var(--ink-faint);
    margin-bottom: 14px;
}

.breadcrumb a {
    color: var(--ink-soft);
    font-weight: 600;
}

.page-title {
    font-size: 1.5rem;
    margin-bottom: 8px;
}

.page-desc {
    color: var(--ink-soft);
    font-size: 0.9rem;
    margin-bottom: 26px;
}

.chapter-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 14px;
}

@media (max-width: 600px) {
    .chapter-list {
        grid-template-columns: 1fr;
    }
}

.chapter-card {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    border: 1px solid var(--card-border);
    background: var(--panel-bg);
    border-radius: 10px;
    padding: 14px 16px;
    transition: transform 0.15s;
}

.chapter-card:hover {
    transform: translateY(-3px);
}

.chapter-card .idx {
    font-family: 'Lalezar', sans-serif;
    font-size: 1.6rem;
    color: var(--accent);
    flex: none;
}

.chapter-card h4 {
    font-size: 0.92rem;
}

.placeholder-box {
    border: 1.5px dashed var(--card-border);
    border-radius: 12px;
    padding: 34px 20px;
    text-align: center;
    color: var(--ink-faint);
    font-size: 0.92rem;
}

.formula-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.formula-item {
    border: 1px solid var(--card-border);
    background: var(--panel-bg);
    border-radius: 10px;
    padding: 14px 16px;
}

.formula-item h4 {
    font-size: 0.92rem;
    margin-bottom: 6px;
    color: var(--accent);
}

.formula-item p {
    font-size: 0.85rem;
    color: var(--ink-soft);
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: 10px;
    padding: 11px 20px;
    font-size: 0.88rem;
    font-weight: 700;
}

.btn.ghost {
    background: transparent;
    color: var(--accent);
    border: 1.5px solid var(--accent);
}

.lesson-head {
    display: flex;
    align-items: center;
    gap: 14px;
    margin-bottom: 24px;
}

.lesson-num {
    font-size: 2.2rem;
    color: var(--accent);
    flex: none;
}

.lesson-body h2 {
    font-size: 1.15rem;
    margin: 26px 0 12px;
    color: var(--ink);
}

.lesson-body h3 {
    font-size: 1.02rem;
    margin: 20px 0 10px;
    color: var(--accent);
}

.lesson-body p {
    font-size: 0.92rem;
    color: var(--ink-soft);
    margin-bottom: 10px;
}

.lesson-body ul,
.lesson-body ol {
    padding-right: 22px;
    margin-bottom: 14px;
}

.lesson-body li {
    font-size: 0.92rem;
    color: var(--ink-soft);
    margin-bottom: 6px;
}

.lesson-body strong {
    color: var(--ink);
}

.formula-box {
    background: var(--paper-2);
    border-right: 4px solid var(--accent);
    border-radius: 8px;
    padding: 14px 16px;
    margin: 14px 0;
}

.formula-box p {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    color: var(--ink);
    margin-bottom: 6px;
}

.info-box {
    background: color-mix(in srgb, var(--accent) 12%, var(--paper-2));
    border-right: 4px solid var(--red);
    border-radius: 8px;
    padding: 14px 16px;
    margin: 14px 0;
    font-size: 0.9rem;
    color: var(--ink-soft);
}

.rule-box {
    border: 1px solid var(--card-border);
    background: var(--panel-bg);
    border-radius: 10px;
    padding: 14px 16px;
    margin: 14px 0;
}

.rule-box p {
    margin-top: 6px;
}

.example-box {
    border: 1.5px dashed var(--card-border);
    border-radius: 8px;
    padding: 12px 14px;
    margin-top: 10px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    color: var(--ink);
}

.table-box {
    border: 1px solid var(--card-border);
    border-radius: 10px;
    overflow: hidden;
    margin: 14px 0;
}

.table-row {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    align-items: center;
    gap: 10px;
    padding: 10px 14px;
    font-size: 0.88rem;
    border-bottom: 1px solid var(--card-border);
}

.table-row:last-child {
    border-bottom: none;
}

.table-row span:nth-child(2) {
    color: var(--accent);
    font-weight: 700;
}

footer {
    border-top: 2px dashed var(--grid);
    padding: 24px 0;
    text-align: center;
    color: var(--ink-faint);
    font-size: 0.8rem;
}