:root {
  --ink: #18222f;
  --muted: #5d6b7c;
  --navy: #10233f;
  --blue: #2563eb;
  --blue-deep: #1747b0;
  --aqua: #18a999;
  --cream: #f8fafc;
  --panel: #ffffff;
  --line: #dce4ef;
  --soft-blue: #edf4ff;
  --soft-aqua: #eafaf7;
  --danger: #b42318;
  --success: #087a5b;
  --shadow: 0 18px 45px rgba(16, 35, 63, .09);
  --radius: 22px;
  --content: 1180px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 92px; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--cream);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 17px;
  line-height: 1.7;
}
body.chat-open { overflow: hidden; }
a { color: inherit; }
button, input, textarea { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
:focus-visible { outline: 3px solid #f4b740; outline-offset: 3px; }
.skip-link { position: fixed; z-index: 200; top: 8px; left: 8px; transform: translateY(-150%); padding: 10px 16px; background: var(--navy); color: white; border-radius: 10px; }
.skip-link:focus { transform: none; }
.container { width: min(calc(100% - 36px), var(--content)); margin-inline: auto; }
.eyebrow { margin: 0 0 8px; color: var(--blue); font-size: .78rem; font-weight: 800; letter-spacing: .12em; text-transform: uppercase; }
.muted { color: var(--muted); }
.pill { display: inline-flex; align-items: center; gap: 7px; padding: 6px 11px; border: 1px solid var(--line); border-radius: 999px; background: white; color: var(--muted); font-size: .82rem; font-weight: 700; }

.site-header { position: sticky; z-index: 100; top: 0; border-bottom: 1px solid rgba(220,228,239,.9); background: rgba(248,250,252,.92); backdrop-filter: blur(16px); }
.nav-wrap { min-height: 76px; display: flex; align-items: center; justify-content: space-between; gap: 24px; }
.brand { display: inline-flex; align-items: center; gap: 11px; text-decoration: none; font-weight: 850; letter-spacing: -.02em; }
.brand-mark { display: grid; place-items: center; width: 38px; height: 38px; border-radius: 13px; color: white; background: linear-gradient(135deg, var(--blue), var(--aqua)); box-shadow: 0 8px 22px rgba(37,99,235,.24); }
.brand-mark svg { width: 22px; height: 22px; }
.brand small { display: block; color: var(--muted); font-size: .68rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; }
.nav-links { display: flex; align-items: center; gap: 5px; }
.nav-links a { padding: 9px 12px; border-radius: 10px; color: #334155; font-size: .92rem; font-weight: 700; text-decoration: none; }
.nav-links a:hover, .nav-links a[aria-current="page"] { color: var(--blue); background: var(--soft-blue); }
.nav-toggle { display: none; border: 0; background: transparent; padding: 9px; border-radius: 10px; }
.nav-toggle svg { display: block; width: 24px; height: 24px; }

.button { display: inline-flex; min-height: 46px; align-items: center; justify-content: center; gap: 9px; padding: 10px 17px; border: 1px solid transparent; border-radius: 12px; font-weight: 800; text-decoration: none; cursor: pointer; transition: transform .18s ease, box-shadow .18s ease, background .18s ease; }
.button:hover { transform: translateY(-1px); }
.button-primary { color: white; background: var(--blue); box-shadow: 0 10px 25px rgba(37,99,235,.22); }
.button-primary:hover { background: var(--blue-deep); }
.button-secondary { color: var(--navy); background: white; border-color: var(--line); }
.button-quiet { min-height: 40px; padding: 7px 12px; color: var(--blue); background: var(--soft-blue); border-color: #cfe0ff; font-size: .9rem; }

.hero { position: relative; overflow: hidden; padding: 86px 0 74px; background: radial-gradient(circle at 80% 15%, rgba(24,169,153,.15), transparent 30%), radial-gradient(circle at 10% 0, rgba(37,99,235,.13), transparent 34%); }
.hero-grid { display: grid; grid-template-columns: 1.12fr .88fr; align-items: center; gap: 60px; }
.hero h1, .lesson-hero h1 { max-width: 850px; margin: 12px 0 20px; color: var(--navy); font-size: clamp(2.6rem, 6vw, 5.5rem); line-height: 1.02; letter-spacing: -.055em; }
.hero h1 span { color: var(--blue); }
.hero-copy { max-width: 680px; margin: 0 0 28px; color: #46576a; font-size: clamp(1.08rem, 2vw, 1.3rem); line-height: 1.65; }
.button-row { display: flex; flex-wrap: wrap; gap: 12px; }
.hero-card { position: relative; padding: 26px; border: 1px solid rgba(220,228,239,.9); border-radius: 28px; background: rgba(255,255,255,.85); box-shadow: var(--shadow); }
.hero-card::before { content: ""; position: absolute; width: 80px; height: 80px; top: -18px; right: -18px; border-radius: 24px; background: linear-gradient(135deg, var(--blue), var(--aqua)); transform: rotate(12deg); z-index: -1; }
.mini-lesson { padding: 20px; border-radius: 17px; background: var(--navy); color: white; }
.mini-lesson p { margin: 0; color: #cbd8e7; }
.mini-lesson strong { display: block; margin: 6px 0 3px; font-size: 1.28rem; }
.ai-preview { margin-top: 16px; display: grid; gap: 11px; }
.bubble { width: fit-content; max-width: 91%; padding: 12px 15px; border-radius: 15px 15px 15px 4px; background: #eef4ff; color: #20324a; font-size: .94rem; }
.bubble.user { justify-self: end; border-radius: 15px 15px 4px 15px; background: var(--blue); color: white; }

.section { padding: 84px 0; }
.section-alt { background: white; }
.section-head { max-width: 720px; margin-bottom: 34px; }
.section-head h2 { margin: 0 0 10px; color: var(--navy); font-size: clamp(2rem, 4vw, 3.2rem); line-height: 1.12; letter-spacing: -.04em; }
.section-head p { margin: 0; color: var(--muted); font-size: 1.05rem; }
.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.feature-card, .tense-card { border: 1px solid var(--line); border-radius: var(--radius); background: var(--panel); box-shadow: 0 12px 28px rgba(16,35,63,.05); }
.feature-card { padding: 25px; }
.feature-icon { display: grid; place-items: center; width: 45px; height: 45px; margin-bottom: 18px; border-radius: 14px; color: var(--blue); background: var(--soft-blue); font-weight: 900; }
.feature-card h3 { margin: 0 0 8px; color: var(--navy); }
.feature-card p { margin: 0; color: var(--muted); }
.tense-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 16px; }
.tense-card { position: relative; min-height: 190px; padding: 21px; text-decoration: none; transition: transform .18s, border-color .18s, box-shadow .18s; }
.tense-card.available:hover { transform: translateY(-4px); border-color: #a8c6ff; box-shadow: var(--shadow); }
.tense-card .number { color: #8da0b6; font-size: .8rem; font-weight: 800; }
.tense-card h3 { margin: 20px 0 8px; color: var(--navy); font-size: 1.08rem; line-height: 1.35; }
.tense-card p { margin: 0; color: var(--muted); font-size: .9rem; line-height: 1.5; }
.status { position: absolute; top: 18px; right: 18px; padding: 4px 9px; border-radius: 999px; color: #6a7481; background: #edf1f5; font-size: .69rem; font-weight: 850; text-transform: uppercase; letter-spacing: .06em; }
.status.live { color: var(--success); background: var(--soft-aqua); }

.lesson-hero { padding: 58px 0 38px; background: radial-gradient(circle at 85% 10%, rgba(24,169,153,.14), transparent 28%), linear-gradient(180deg, white, var(--cream)); }
.breadcrumb { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; color: var(--muted); font-size: .88rem; }
.breadcrumb a { color: var(--blue); text-decoration: none; }
.lesson-hero h1 { margin-top: 24px; font-size: clamp(2.7rem, 6vw, 4.9rem); }
.lesson-lede { max-width: 760px; color: #42546a; font-size: 1.2rem; }
.lesson-example { display: inline-flex; align-items: center; gap: 10px; margin: 12px 0 26px; padding: 12px 15px; border: 1px solid #cfe0ff; border-radius: 12px; background: var(--soft-blue); font-weight: 750; }
.progress-strip { padding: 16px 0; border-block: 1px solid var(--line); background: white; }
.progress-flow { display: flex; align-items: center; gap: 8px; overflow-x: auto; scrollbar-width: thin; }
.progress-flow span { flex: 0 0 auto; color: #617085; font-size: .74rem; font-weight: 850; letter-spacing: .06em; text-transform: uppercase; }
.progress-flow i { color: #b5c0cd; font-style: normal; }
.lesson-layout { display: grid; grid-template-columns: 250px minmax(0, 1fr); gap: 34px; align-items: start; padding-block: 46px 90px; }
.lesson-nav { position: sticky; top: 104px; padding: 18px; border: 1px solid var(--line); border-radius: 18px; background: white; }
.lesson-nav strong { display: block; margin: 0 0 10px; color: var(--navy); }
.lesson-nav a { display: block; padding: 7px 9px; border-radius: 8px; color: var(--muted); font-size: .83rem; font-weight: 700; line-height: 1.35; text-decoration: none; }
.lesson-nav a:hover { color: var(--blue); background: var(--soft-blue); }
.lesson-content { min-width: 0; display: grid; gap: 22px; }
.lesson-section { padding: clamp(24px, 4vw, 39px); border: 1px solid var(--line); border-radius: var(--radius); background: white; box-shadow: 0 10px 30px rgba(16,35,63,.04); }
.section-label { display: flex; align-items: center; gap: 10px; margin-bottom: 10px; color: var(--blue); font-size: .78rem; font-weight: 850; text-transform: uppercase; letter-spacing: .09em; }
.section-label span { display: grid; place-items: center; width: 28px; height: 28px; border-radius: 9px; background: var(--soft-blue); }
.lesson-section h2 { margin: 0 0 14px; color: var(--navy); font-size: clamp(1.65rem, 3vw, 2.25rem); line-height: 1.2; letter-spacing: -.025em; }
.lesson-section h3 { margin: 26px 0 10px; color: var(--navy); font-size: 1.1rem; }
.lesson-section p { margin: 0 0 14px; }
.lesson-section ul { padding-left: 1.25rem; }
.timeline { display: grid; grid-template-columns: 1fr auto 1fr auto 1fr; align-items: center; gap: 10px; margin: 24px 0 8px; text-align: center; }
.timeline-line { height: 3px; background: #bfcee0; }
.timeline-point { display: grid; place-items: center; width: 40px; height: 40px; border: 5px solid var(--soft-blue); border-radius: 50%; color: white; background: var(--blue); font-size: .7rem; font-weight: 900; }
.use-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px; }
.use-card { padding: 18px; border: 1px solid var(--line); border-radius: 15px; background: #fbfdff; }
.use-card h3 { margin: 0 0 7px; }
.use-card p { color: var(--muted); font-size: .94rem; }
.examples { display: grid; gap: 8px; }
.example { padding: 12px 14px; border-left: 4px solid var(--aqua); border-radius: 0 10px 10px 0; background: #f4fbfa; }
.formula { margin: 16px 0; padding: 18px; border-radius: 16px; background: var(--navy); color: white; font-size: clamp(1.02rem, 2.1vw, 1.25rem); font-weight: 800; letter-spacing: .01em; overflow-wrap: anywhere; }
.formula .accent { color: #70e2d4; }
.split { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.rule-box { padding: 18px; border: 1px solid #cfe0ff; border-radius: 15px; background: var(--soft-blue); }
.rule-box p:last-child { margin-bottom: 0; }
.table-wrap { overflow-x: auto; }
table { width: 100%; border-collapse: collapse; min-width: 620px; }
th, td { padding: 13px 14px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
th { color: var(--navy); background: #f2f6fb; font-size: .85rem; }
.mistake-list { display: grid; gap: 14px; }
.mistake { padding: 18px; border: 1px solid var(--line); border-radius: 15px; background: #fff; }
.wrong { color: var(--danger); font-weight: 800; }
.correct { color: var(--success); font-weight: 800; }
.why { margin-bottom: 0 !important; color: var(--muted); }
.compare-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.compare-card { padding: 19px; border: 1px solid var(--line); border-radius: 16px; }
.compare-card:first-child { background: var(--soft-blue); }
.compare-card:last-child { background: var(--soft-aqua); }
.practice-list { display: grid; gap: 14px; }
.practice-item { padding: 18px; border: 1px solid var(--line); border-radius: 15px; background: #fbfdff; }
.practice-type { margin: 0 0 4px; color: var(--blue); font-size: .72rem; font-weight: 850; text-transform: uppercase; letter-spacing: .08em; }
.answer { display: none; margin-top: 13px; padding: 12px 14px; border-radius: 10px; color: #075e48; background: var(--soft-aqua); }
.answer.visible { display: block; }
.ai-actions { display: flex; flex-wrap: wrap; gap: 9px; margin-top: 20px; }

.ai-fab { position: fixed; z-index: 120; right: 22px; bottom: 22px; display: flex; align-items: center; gap: 10px; min-height: 55px; padding: 11px 18px 11px 12px; border: 0; border-radius: 999px; color: white; background: var(--blue); box-shadow: 0 14px 40px rgba(17,59,150,.35); font-weight: 850; cursor: pointer; }
.ai-fab .bot { display: grid; place-items: center; width: 33px; height: 33px; border-radius: 50%; color: var(--blue); background: white; }
.chat-backdrop { position: fixed; z-index: 125; inset: 0; display: none; background: rgba(10,24,43,.42); }
.chat-backdrop.visible { display: block; }
.chat-panel { position: fixed; z-index: 130; top: 0; right: 0; width: min(440px, 100%); height: 100dvh; display: flex; flex-direction: column; background: white; box-shadow: -20px 0 50px rgba(10,24,43,.2); transform: translateX(105%); transition: transform .25s ease; }
.chat-panel.open { transform: translateX(0); }
.chat-head { display: flex; justify-content: space-between; align-items: center; gap: 15px; padding: 20px; border-bottom: 1px solid var(--line); }
.chat-head strong { display: block; color: var(--navy); }
.chat-head small { color: var(--muted); }
.icon-button { display: grid; place-items: center; width: 40px; height: 40px; border: 1px solid var(--line); border-radius: 11px; background: white; cursor: pointer; }
.chat-context { padding: 12px 20px; color: #3d536e; background: var(--soft-blue); font-size: .82rem; }
.chat-messages { flex: 1; overflow-y: auto; padding: 20px; }
.chat-welcome { padding: 17px; border-radius: 16px; background: #f4f7fb; color: #43556a; }
.chat-quick { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 13px; }
.chat-quick button { padding: 7px 10px; border: 1px solid #cfe0ff; border-radius: 999px; color: var(--blue); background: white; font-size: .78rem; font-weight: 750; cursor: pointer; }
.chat-form { padding: 15px; border-top: 1px solid var(--line); background: white; }
.chat-form textarea { width: 100%; min-height: 78px; resize: vertical; padding: 12px; border: 1px solid #bac7d6; border-radius: 12px; color: var(--ink); }
.chat-form-row { display: flex; justify-content: space-between; align-items: center; gap: 10px; margin-top: 9px; }
.chat-form-row small { color: var(--muted); font-size: .72rem; }

.site-footer { padding: 62px 0 28px; color: #d8e2ee; background: var(--navy); }
.footer-grid { display: grid; grid-template-columns: 1.3fr .7fr; gap: 50px; }
.site-footer .brand { color: white; }
.footer-copy { max-width: 630px; color: #b6c6d8; }
.footer-actions { display: grid; align-content: start; gap: 10px; }
.footer-actions a { color: white; text-decoration: none; font-weight: 750; }
.footer-actions a:hover { color: #7ce5d8; }
.footer-bottom { margin-top: 42px; padding-top: 22px; border-top: 1px solid rgba(255,255,255,.13); display: flex; justify-content: space-between; gap: 20px; color: #9fb1c6; font-size: .85rem; }

@media (max-width: 960px) {
  .hero-grid { grid-template-columns: 1fr; gap: 40px; }
  .hero-card { max-width: 650px; }
  .tense-grid { grid-template-columns: repeat(3, 1fr); }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-nav { position: static; display: flex; gap: 5px; overflow-x: auto; }
  .lesson-nav strong { display: none; }
  .lesson-nav a { flex: 0 0 auto; }
}
@media (max-width: 760px) {
  body { font-size: 16px; }
  .nav-toggle { display: block; }
  .nav-links { position: absolute; top: 76px; left: 18px; right: 18px; display: none; padding: 10px; border: 1px solid var(--line); border-radius: 16px; background: white; box-shadow: var(--shadow); }
  .nav-links.open { display: grid; }
  .hero { padding-top: 56px; }
  .feature-grid, .tense-grid, .use-grid { grid-template-columns: repeat(2, 1fr); }
  .split, .compare-grid, .footer-grid { grid-template-columns: 1fr; }
  .timeline { grid-template-columns: auto 1fr auto 1fr auto; }
  .footer-bottom { flex-direction: column; }
}
@media (max-width: 520px) {
  .container { width: min(calc(100% - 24px), var(--content)); }
  .section { padding: 62px 0; }
  .feature-grid, .tense-grid { grid-template-columns: 1fr; }
  .tense-card { min-height: 155px; }
  .lesson-section { border-radius: 17px; }
  .ai-fab { right: 13px; bottom: 13px; padding-right: 13px; }
  .ai-fab .label { display: none; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition-duration: .01ms !important; animation-duration: .01ms !important; animation-iteration-count: 1 !important; }
}