:root {
    --color-ink: #17212b;
    --color-muted: #536271;
    --color-page: #f7faf8;
    --color-surface: #ffffff;
    --color-line: #d9e4df;
    --color-brand: #155b63;
    --color-brand-strong: #0f4248;
    --color-accent: #b43f28;
    --color-accent-soft: #fff0dc;
    --color-success-soft: #e6f4ea;
    --color-focus: #f7c948;
    --shadow-soft: 0 14px 40px rgba(23, 33, 43, 0.08);
    --radius: 8px;
    --page-width: 1120px;
}

* {
    box-sizing: border-box;
}

html {
    color-scheme: light;
}

body {
    margin: 0;
    background: var(--color-page);
    color: var(--color-ink);
    font-family: Arial, Helvetica, sans-serif;
    font-size: 17px;
    line-height: 1.6;
}

img {
    max-width: 100%;
    height: auto;
}

a {
    color: var(--color-brand);
    text-underline-offset: 0.18em;
}

a:hover {
    color: var(--color-accent);
}

:focus-visible {
    outline: 3px solid var(--color-focus);
    outline-offset: 3px;
}

.skip-link {
    position: absolute;
    left: 1rem;
    top: 1rem;
    z-index: 10;
    transform: translateY(-150%);
    border-radius: var(--radius);
    background: var(--color-ink);
    color: #fff;
    padding: 0.55rem 0.8rem;
}

.skip-link:focus {
    transform: translateY(0);
}

.site-shell {
    min-height: 100vh;
}

.site-header {
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-line);
}

.site-header__inner,
.site-nav__list,
.site-main,
.site-footer__inner,
.ad-placeholder {
    width: min(100% - 2rem, var(--page-width));
    margin-inline: auto;
}

.site-header__inner {
    padding: 1rem 0;
}

.brand {
    display: inline-flex;
    align-items: center;
    gap: 0.85rem;
    color: var(--color-ink);
    text-decoration: none;
}

.brand__mark {
    width: 58px;
    height: 58px;
    border-radius: 50%;
    object-fit: cover;
}

.brand__text {
    display: grid;
}

.brand__name {
    font-size: 1.65rem;
    font-weight: 800;
    line-height: 1.1;
}

.brand__tagline {
    color: var(--color-muted);
    font-size: 0.95rem;
}

.site-nav {
    position: sticky;
    top: 0;
    z-index: 5;
    border-bottom: 1px solid var(--color-line);
    background: rgba(247, 250, 248, 0.94);
    backdrop-filter: blur(10px);
}

.site-nav__list {
    display: flex;
    flex-wrap: wrap;
    gap: 0.35rem;
    list-style: none;
    padding: 0.65rem 0;
}

.site-nav__link {
    display: inline-flex;
    min-height: 2.35rem;
    align-items: center;
    border-radius: var(--radius);
    color: var(--color-ink);
    font-weight: 700;
    padding: 0.4rem 0.7rem;
    text-decoration: none;
}

.site-nav__link:hover,
.site-nav__link.is-active {
    background: var(--color-brand);
    color: #fff;
}

.site-main {
    padding: 2rem 0 1.5rem;
}

.hero {
    display: grid;
    grid-template-columns: minmax(0, 1.45fr) minmax(260px, 0.75fr);
    gap: 1.5rem;
    align-items: stretch;
    padding: 2rem 0 1rem;
}

.page-hero {
    max-width: 820px;
    padding: 2rem 0 1rem;
}

.hero__content {
    align-self: center;
}

.eyebrow {
    color: var(--color-accent);
    font-size: 0.9rem;
    font-weight: 800;
    letter-spacing: 0;
    margin: 0 0 0.45rem;
    text-transform: uppercase;
}

h1,
h2,
h3 {
    color: var(--color-ink);
    line-height: 1.18;
    margin: 0;
}

h1 {
    font-size: clamp(2.2rem, 2.2rem + 1vw, 3.35rem);
    max-width: 12ch;
}

h2 {
    font-size: 1.75rem;
    margin-bottom: 0.8rem;
}

h3 {
    font-size: 1.15rem;
}

.lede {
    color: var(--color-muted);
    font-size: 1.15rem;
    max-width: 62ch;
}

.button-row {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 1.25rem;
}

.button {
    display: inline-flex;
    min-height: 2.75rem;
    align-items: center;
    justify-content: center;
    border: 2px solid var(--color-brand);
    border-radius: var(--radius);
    background: var(--color-brand);
    color: #fff;
    font-weight: 800;
    padding: 0.55rem 0.9rem;
    text-decoration: none;
}

.button:hover {
    border-color: var(--color-accent);
    background: var(--color-accent);
    color: #fff;
}

.button--secondary {
    background: transparent;
    color: var(--color-brand);
}

.button--secondary:hover {
    background: var(--color-brand);
    color: #fff;
}

.quick-panel {
    align-self: center;
    border: 1px solid var(--color-line);
    border-radius: var(--radius);
    background: var(--color-surface);
    box-shadow: var(--shadow-soft);
    padding: 1.2rem;
}

.quick-panel ul,
.resource-card ul,
.check-list {
    margin: 0.75rem 0 0;
    padding-left: 1.2rem;
}

.quick-panel li + li,
.resource-card li + li,
.check-list li + li {
    margin-top: 0.4rem;
}

.section {
    padding: 2rem 0;
}

.section__intro {
    color: var(--color-muted);
    margin-top: 0;
    max-width: 72ch;
}

.resource-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 1rem;
}

.resource-card {
    border: 1px solid var(--color-line);
    border-radius: var(--radius);
    background: var(--color-surface);
    padding: 1rem;
}

.resource-card__meta {
    color: var(--color-muted);
    font-size: 0.92rem;
    margin: 0.2rem 0 0;
}

.callout {
    border-left: 5px solid var(--color-accent);
    border-radius: var(--radius);
    background: var(--color-accent-soft);
    margin: 1rem 0 0;
    padding: 1rem;
}

.callout p {
    margin: 0;
}

.link-list {
    display: flex;
    flex-wrap: wrap;
    gap: 0.55rem;
    margin-top: 1rem;
}

.link-list a {
    border: 1px solid var(--color-line);
    border-radius: var(--radius);
    background: var(--color-surface);
    font-weight: 700;
    padding: 0.45rem 0.7rem;
    text-decoration: none;
}

.lesson-article {
    max-width: 880px;
}

.lesson-article h1 {
    max-width: 18ch;
}

.lesson-section {
    padding: 1.35rem 0;
}

.lesson-section + .lesson-section {
    border-top: 1px solid var(--color-line);
}

.lesson-section h2 {
    margin-bottom: 0.65rem;
}

.lesson-section h3 {
    margin: 1rem 0 0.35rem;
}

.steps,
.practice-list,
.answer-key {
    margin: 0.75rem 0 0;
    padding-left: 1.4rem;
}

.steps li + li,
.practice-list li + li,
.answer-key li + li {
    margin-top: 0.45rem;
}

.example-box {
    border: 1px solid var(--color-line);
    border-radius: var(--radius);
    background: var(--color-surface);
    margin: 1rem 0;
    padding: 1rem;
}

.math-work {
    background: #f0f6f4;
    border-radius: var(--radius);
    overflow-x: auto;
    padding: 0.85rem;
    white-space: pre;
}

.common-mistakes {
    border-left: 5px solid var(--color-brand);
    border-radius: var(--radius);
    background: #edf7f8;
    padding: 1rem;
}

.ad-placeholder {
    border: 1px dashed #9eaaa4;
    border-radius: var(--radius);
    color: var(--color-muted);
    margin-bottom: 1.5rem;
    padding: 0.9rem;
    text-align: center;
}

.site-footer {
    border-top: 1px solid var(--color-line);
    background: var(--color-surface);
}

.site-footer__inner {
    display: flex;
    flex-wrap: wrap;
    gap: 0.7rem 1rem;
    justify-content: space-between;
    padding: 1.2rem 0;
}

.site-footer p {
    margin: 0;
}

.site-footer nav {
    display: flex;
    flex-wrap: wrap;
    gap: 0.85rem;
}

@media (max-width: 860px) {
    .hero,
    .resource-grid {
        grid-template-columns: 1fr;
    }

    h1 {
        max-width: 16ch;
    }
}

@media (max-width: 560px) {
    body {
        font-size: 16px;
    }

    .site-header__inner,
    .site-nav__list,
    .site-main,
    .site-footer__inner,
    .ad-placeholder {
        width: min(100% - 1rem, var(--page-width));
    }

    .brand__mark {
        width: 48px;
        height: 48px;
    }

    .brand__name {
        font-size: 1.35rem;
    }

    .brand__tagline {
        font-size: 0.85rem;
    }

    .site-nav__list {
        flex-wrap: nowrap;
        overflow-x: auto;
        padding-bottom: 0.8rem;
    }

    .site-nav__link {
        white-space: nowrap;
    }

    .button {
        width: 100%;
    }
}

@media print {
    body {
        background: #fff;
        color: #000;
        font-size: 12pt;
    }

    .skip-link,
    .site-nav,
    .ad-placeholder,
    .button-row {
        display: none;
    }

    .site-header,
    .site-footer {
        border-color: #999;
    }

    a {
        color: #000;
    }
}