:root {
  --ink: #17332c;
  --muted: #63726d;
  --primary: #246b54;
  --primary-dark: #18513e;
  --accent: #e9a23b;
  --cream: #f7f4ec;
  --paper: #ffffff;
  --line: #dfe6e2;
  --notice: #fff8e7;
  --shadow: 0 14px 40px rgba(27, 68, 54, 0.09);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--cream);
  font-family: "Be Vietnam Pro", system-ui, sans-serif;
  line-height: 1.6;
}

img {
  display: block;
  max-width: 100%;
}

.site-header {
  position: sticky;
  z-index: 10;
  top: 0;
  border-bottom: 1px solid rgba(23, 51, 44, 0.08);
  background: rgba(247, 244, 236, 0.9);
  backdrop-filter: blur(14px);
}

.header-inner,
main,
footer {
  width: min(1120px, calc(100% - 40px));
  margin-inline: auto;
}

.header-inner {
  display: flex;
  min-height: 72px;
  align-items: center;
  justify-content: space-between;
}

.brand,
.nav-link {
  color: inherit;
  text-decoration: none;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
}

.brand-mark {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border-radius: 50%;
  color: white;
  background: var(--primary);
  font-size: 20px;
}

.nav-link {
  color: var(--primary-dark);
  font-size: 14px;
  font-weight: 600;
}

.hero {
  max-width: 780px;
  padding: 92px 0 56px;
}

.eyebrow {
  margin: 0 0 12px;
  color: var(--primary);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 22px;
  font-size: clamp(42px, 7vw, 76px);
  line-height: 1.08;
  letter-spacing: -0.055em;
}

h1 span {
  color: var(--primary);
}

.intro {
  max-width: 650px;
  margin-bottom: 0;
  color: var(--muted);
  font-size: clamp(16px, 2vw, 19px);
}

.notice {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  margin-bottom: 88px;
  padding: 20px 22px;
  border: 1px solid #f0dba8;
  border-radius: 16px;
  background: var(--notice);
}

.notice-icon {
  display: grid;
  flex: 0 0 auto;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 50%;
  color: #6b4b12;
  background: #f7d889;
  font-family: Georgia, serif;
  font-weight: 700;
}

.notice strong {
  display: block;
  margin-bottom: 2px;
}

.notice p {
  margin-bottom: 0;
  color: #6d6148;
  font-size: 14px;
}

.lesson-list {
  scroll-margin-top: 96px;
}

.section-heading {
  margin-bottom: 30px;
}

h2 {
  margin-bottom: 0;
  font-size: clamp(30px, 4vw, 44px);
  line-height: 1.15;
  letter-spacing: -0.04em;
}

.lesson-grid {
  display: grid;
  gap: 28px;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.lesson-card {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 22px;
  background: var(--paper);
  box-shadow: var(--shadow);
}

.video-frame {
  position: relative;
  display: grid;
  aspect-ratio: 16 / 9;
  place-items: center;
  overflow: hidden;
  background: linear-gradient(145deg, #193d33, #102a23);
}

.video-frame iframe {
  width: 100%;
  height: 100%;
  border: 0;
}

.video-placeholder {
  position: relative;
  display: grid;
  width: 100%;
  height: 100%;
  place-items: center;
  padding: 24px;
  color: #dce9e4;
  text-align: center;
}

.video-link {
  align-content: center;
  color: white;
  text-decoration: none;
}

.video-thumbnail {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  opacity: 0.45;
}

.play-icon {
  position: relative;
  z-index: 1;
  width: 64px;
  height: 46px;
  margin-bottom: 14px;
  border-radius: 13px;
  background: #e6433a;
}

.play-icon::after {
  position: absolute;
  top: 50%;
  left: 52%;
  border-top: 9px solid transparent;
  border-bottom: 9px solid transparent;
  border-left: 14px solid white;
  content: "";
  transform: translate(-50%, -50%);
}

.video-placeholder p {
  position: relative;
  z-index: 1;
  margin-bottom: 0;
  font-size: 14px;
}

.video-link:hover .play-icon {
  transform: scale(1.06);
}

.video-link:focus-visible {
  outline: 3px solid rgba(255, 255, 255, 0.8);
  outline-offset: -5px;
}

.card-body {
  padding: 22px;
}

.lesson-number {
  margin-bottom: 6px;
  color: var(--primary);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

h3 {
  margin-bottom: 18px;
  font-size: 23px;
  line-height: 1.25;
  letter-spacing: -0.025em;
}

.sheet-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 10px;
  color: var(--muted);
  font-size: 13px;
  font-weight: 600;
}

.sheet-label span:last-child {
  color: var(--primary);
  font-weight: 500;
}

.sheet-link {
  display: block;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fbfbf8;
}

.sheet-link img {
  width: 100%;
  height: auto;
  transition: transform 180ms ease;
}

.sheet-link:hover img {
  transform: scale(1.015);
}

.sheet-link:focus-visible,
.nav-link:focus-visible,
.brand:focus-visible {
  outline: 3px solid rgba(36, 107, 84, 0.35);
  outline-offset: 3px;
}

footer {
  padding: 72px 0 34px;
  color: var(--muted);
  font-size: 13px;
  text-align: center;
}

footer p {
  margin-bottom: 0;
}

@media (max-width: 740px) {
  .header-inner,
  main,
  footer {
    width: min(100% - 28px, 1120px);
  }

  .header-inner {
    min-height: 64px;
  }

  .hero {
    padding: 64px 0 42px;
  }

  .notice {
    margin-bottom: 64px;
  }

  .lesson-grid {
    grid-template-columns: 1fr;
  }

  .lesson-card {
    border-radius: 18px;
  }

  .card-body {
    padding: 18px;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  .sheet-link img {
    transition: none;
  }
}