* {
  box-sizing: border-box;
}

:root {
  --ink: #1f282d;
  --muted: #5e6d76;
  --paper: #f7f4ec;
  --white: #ffffff;
  --teal: #2a5b68;
  --teal-dark: #163f4b;
  --line: #d8d1c4;
  --gold: #a86f2a;
  --soft: #eef3f0;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: "Yu Mincho", "YuMincho", "Hiragino Mincho ProN", "Noto Serif JP", serif;
  line-height: 1.9;
}

a {
  color: var(--teal-dark);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.18em;
}

.site-header {
  position: fixed;
  z-index: 10;
  top: 0;
  left: 0;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px clamp(18px, 4vw, 56px);
  background: rgba(247, 244, 236, 0.9);
  border-bottom: 1px solid rgba(31, 40, 45, 0.08);
  backdrop-filter: blur(10px);
}

.brand {
  font-weight: 700;
  text-decoration: none;
}

nav {
  display: flex;
  gap: clamp(12px, 3vw, 28px);
  font-size: 14px;
}

nav a {
  text-decoration: none;
}

.hero {
  min-height: 76vh;
  display: grid;
  place-items: center;
  padding: 96px clamp(20px, 6vw, 80px) 44px;
  position: relative;
  overflow: hidden;
  background: #1f282d;
}

.hero__image {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(90deg, rgba(31, 40, 45, 0.88), rgba(31, 40, 45, 0.58), rgba(31, 40, 45, 0.24)),
    url("./workbook-preview-page-01.png");
  background-size: cover;
  background-position: center right;
  transform: scale(1.02);
}

.hero__content {
  position: relative;
  width: min(920px, 100%);
  color: var(--white);
}

.eyebrow {
  margin: 0 0 12px;
  color: var(--gold);
  font-family: "Yu Gothic", "YuGothic", sans-serif;
  font-size: 13px;
  font-weight: 700;
}

.hero .eyebrow {
  color: #e4b46f;
}

h1, h2, h3 {
  margin: 0;
  line-height: 1.35;
  letter-spacing: 0;
}

h1 {
  max-width: 760px;
  font-size: clamp(36px, 7vw, 72px);
  font-weight: 700;
}

h2 {
  font-size: clamp(26px, 4.2vw, 44px);
}

h3 {
  font-size: 20px;
}

.lead {
  max-width: 660px;
  margin: 22px 0 30px;
  font-size: clamp(17px, 2.4vw, 22px);
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 12px 20px;
  border: 0;
  border-radius: 6px;
  background: var(--teal);
  color: var(--white);
  font-family: "Yu Gothic", "YuGothic", sans-serif;
  font-size: 16px;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
}

.button:hover {
  background: var(--teal-dark);
}

.button--wide {
  width: 100%;
}

.section {
  padding: clamp(54px, 8vw, 96px) clamp(20px, 5vw, 64px);
}

.section__inner {
  width: min(1120px, 100%);
  margin: 0 auto;
}

.narrow {
  width: min(760px, 100%);
}

.two-column {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(260px, 0.75fr);
  gap: clamp(28px, 6vw, 72px);
  align-items: center;
}

.preview {
  margin: 0;
}

.preview img {
  display: block;
  width: 100%;
  height: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 22px 60px rgba(31, 40, 45, 0.16);
}

figcaption,
.form-note,
.fallback {
  color: var(--muted);
  font-family: "Yu Gothic", "YuGothic", sans-serif;
  font-size: 14px;
  line-height: 1.7;
}

.receive {
  background: var(--soft);
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.signup {
  display: grid;
  gap: 16px;
  margin-top: 28px;
}

label {
  display: grid;
  gap: 6px;
  font-family: "Yu Gothic", "YuGothic", sans-serif;
  font-weight: 700;
}

input {
  width: 100%;
  min-height: 48px;
  padding: 10px 12px;
  border: 1px solid #b8c2c5;
  border-radius: 6px;
  background: var(--white);
  color: var(--ink);
  font-size: 16px;
}

input:focus {
  outline: 3px solid rgba(42, 91, 104, 0.2);
  border-color: var(--teal);
}

.form-status {
  min-height: 24px;
  margin: 0;
  color: var(--teal-dark);
  font-family: "Yu Gothic", "YuGothic", sans-serif;
  font-weight: 700;
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 16px;
  margin-top: 34px;
}

.feature-grid article {
  min-height: 220px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.56);
}

details {
  padding: 18px 0;
  border-bottom: 1px solid var(--line);
}

summary {
  cursor: pointer;
  font-weight: 700;
}

.site-footer {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 16px;
  padding: 28px clamp(20px, 5vw, 64px);
  color: var(--muted);
  border-top: 1px solid var(--line);
}

.simple-page {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 24px;
}

.simple {
  width: min(720px, 100%);
  padding: clamp(28px, 6vw, 56px);
  background: var(--white);
  border: 1px solid var(--line);
  border-radius: 8px;
}

@media (max-width: 860px) {
  .site-header {
    position: static;
  }

  nav {
    display: none;
  }

  .hero {
    min-height: 70vh;
    padding-top: 52px;
  }

  .hero__image {
    background-position: center;
  }

  .two-column,
  .feature-grid {
    grid-template-columns: 1fr;
  }

  .feature-grid article {
    min-height: auto;
  }
}