:root {
  --ink: #17202a;
  --muted: #647184;
  --line: #d9e1ea;
  --white: #ffffff;
  --blue: #176b87;
  --green: #2f7d65;
  --coral: #c95d43;
  --gold: #a87322;
  --soft-blue: #e9f4f7;
  --soft-green: #edf6f1;
  --soft-coral: #fff0ea;
  --shadow: 0 18px 46px rgba(23, 32, 42, .1);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background:
    linear-gradient(135deg, rgba(23, 107, 135, .1), transparent 34rem),
    linear-gradient(315deg, rgba(47, 125, 101, .12), transparent 30rem),
    #f5f8fa;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
  letter-spacing: 0;
}
a { color: inherit; text-decoration: none; }
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  border-bottom: 1px solid rgba(217, 225, 234, .86);
  background: rgba(251, 252, 253, .92);
  backdrop-filter: blur(14px);
}
.topbar-inner, main {
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
}
.topbar-inner {
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--blue);
  font-weight: 850;
}
.brand-mark {
  width: 34px;
  height: 34px;
  border-radius: 8px;
  background: linear-gradient(135deg, var(--blue), var(--green));
  display: grid;
  place-items: center;
  color: #fff;
  font-size: 16px;
}
.nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 10px;
}
.nav a {
  border: 1px solid rgba(23, 107, 135, .18);
  border-radius: 999px;
  padding: 8px 12px;
  color: #324055;
  background: #fff;
  font-size: 14px;
}
section { padding: clamp(42px, 7vw, 86px) 0; }
.hero {
  min-height: calc(100vh - 64px);
  display: grid;
  align-items: center;
}
.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(320px, .82fr);
  gap: clamp(28px, 6vw, 72px);
  align-items: center;
}
.eyebrow {
  margin: 0 0 16px;
  color: var(--coral);
  font-size: clamp(15px, 1.5vw, 19px);
  font-weight: 850;
  text-transform: uppercase;
}
h1, h2, h3, p { margin: 0; }
h1 {
  max-width: 880px;
  font-size: clamp(42px, 7vw, 88px);
  line-height: 1.04;
  letter-spacing: 0;
}
h2 {
  font-size: clamp(30px, 4.4vw, 58px);
  line-height: 1.12;
  letter-spacing: 0;
}
h3 {
  font-size: clamp(21px, 2vw, 29px);
  line-height: 1.22;
  letter-spacing: 0;
}
p, li {
  color: #344254;
  font-size: clamp(16px, 1.45vw, 21px);
  line-height: 1.65;
}
.lead {
  max-width: 760px;
  margin-top: 22px;
  color: #344254;
  font-size: clamp(20px, 2.2vw, 30px);
  line-height: 1.5;
}
.summary-card, .note-card, .topic-card, .formula-card, .task-card {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--white);
  padding: clamp(18px, 2.4vw, 28px);
}
.summary-card {
  display: grid;
  gap: 18px;
  box-shadow: var(--shadow);
  border-top: 5px solid var(--green);
}
.card-kicker {
  display: inline-flex;
  width: fit-content;
  border-radius: 999px;
  padding: 7px 12px;
  background: var(--soft-green);
  color: var(--green);
  font-weight: 800;
  font-size: 14px;
}
.primary-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: fit-content;
  border-radius: 8px;
  padding: 13px 18px;
  background: var(--green);
  color: #fff;
  font-weight: 800;
}
.section-head {
  display: grid;
  gap: 12px;
  margin-bottom: 26px;
}
.section-head p { max-width: 850px; }
.grid { display: grid; gap: 18px; }
.grid.two { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid.three { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid.four { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.note-card, .topic-card, .formula-card, .task-card { display: grid; gap: 13px; }
.accent-blue { border-top: 5px solid var(--blue); }
.accent-green { border-top: 5px solid var(--green); }
.accent-coral { border-top: 5px solid var(--coral); }
.accent-gold { border-top: 5px solid var(--gold); }
ul { margin: 0; padding-left: 1.2em; }
li + li { margin-top: 7px; }
code {
  border-radius: 6px;
  padding: 2px 6px;
  background: #eef3f7;
  color: #173246;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  font-size: .92em;
}
.chips { display: flex; flex-wrap: wrap; gap: 9px; }
.chip {
  border-radius: 999px;
  padding: 8px 11px;
  border: 1px solid rgba(23, 107, 135, .18);
  background: var(--soft-blue);
  color: #1d5367;
  font-size: 15px;
  font-weight: 750;
}
.formula-card { border-left: 5px solid var(--green); }
.formula { display: flex; flex-wrap: wrap; gap: 10px; }
.formula span {
  border-radius: 8px;
  padding: 10px 12px;
  background: var(--soft-green);
  color: #245a49;
  font-weight: 850;
  font-size: 16px;
}
.example {
  border-radius: 8px;
  padding: 14px 16px;
  background: #f6f8fb;
  border: 1px solid #e5ebf1;
  color: #2c394b;
  font-size: clamp(15px, 1.35vw, 19px);
  line-height: 1.6;
}
.speech-frame {
  display: grid;
  gap: 12px;
  counter-reset: frame;
}
.frame-line {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 12px;
  align-items: start;
  padding: 14px;
  border-radius: 8px;
  background: #fff;
  border: 1px solid var(--line);
}
.frame-line::before {
  counter-increment: frame;
  content: counter(frame);
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--green);
  color: #fff;
  display: grid;
  place-items: center;
  font-weight: 850;
  font-size: 14px;
}
.mini-title {
  color: var(--coral);
  font-weight: 850;
  font-size: 15px;
  text-transform: uppercase;
}
.footer {
  padding: 32px 0 58px;
  color: var(--muted);
  text-align: center;
  font-size: 15px;
}
@media (max-width: 900px) {
  .topbar-inner { align-items: flex-start; flex-direction: column; padding: 12px 0; }
  .nav { justify-content: flex-start; }
  .hero { min-height: auto; }
  .hero-grid, .grid.two, .grid.three, .grid.four { grid-template-columns: 1fr; }
  .primary-link { width: 100%; }
}


/* Homework blocks */
.homework-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: end;
  margin-bottom: 18px;
}
.homework-field {
  display: grid;
  gap: 7px;
  min-width: 240px;
}
.homework-field label {
  color: var(--blue);
  font-size: 15px;
  font-weight: 850;
}
.homework-select,
.homework-button {
  min-height: 44px;
  border: 1px solid rgba(23, 107, 135, .22);
  border-radius: 8px;
  background: #fff;
  color: #243448;
  font: inherit;
  font-weight: 750;
  padding: 9px 12px;
}
.homework-button {
  cursor: pointer;
  background: var(--blue);
  color: #fff;
}
.homework-note {
  color: var(--muted);
  font-size: 15px;
  font-weight: 700;
}
.homework-task {
  border: 1px solid var(--line);
  border-top: 5px solid var(--blue);
  border-radius: 8px;
  background: #fff;
  padding: clamp(16px, 2.2vw, 26px);
  display: grid;
  gap: 12px;
  min-width: 0;
}
.homework-task:nth-child(2n) { border-top-color: var(--green); }
.homework-task:nth-child(3n) { border-top-color: var(--coral); }
.homework-task h3 { color: var(--blue); }
.homework-meta {
  width: fit-content;
  border-radius: 999px;
  padding: 6px 10px;
  background: var(--soft-blue);
  color: var(--blue);
  font-size: 14px;
  font-weight: 850;
}
.homework-list,
.homework-questions {
  margin: 0;
  padding-left: 1.2em;
}
.homework-list li + li,
.homework-questions li + li { margin-top: 7px; }
.homework-bank {
  display: grid;
  gap: 12px;
}
.homework-bank details {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  padding: 15px 18px;
}
.homework-bank summary {
  cursor: pointer;
  color: var(--blue);
  font-size: clamp(19px, 1.8vw, 25px);
  font-weight: 850;
}
.homework-bank details[open] summary { margin-bottom: 12px; }
@media (max-width: 760px) {
  .homework-actions { align-items: stretch; }
  .homework-field,
  .homework-button { width: 100%; }
}