:root {
  --ink: #172033;
  --muted: #647086;
  --paper: #f7f8fc;
  --white: #ffffff;
  --line: #dfe4ef;
  --indigo: #4e46e5;
  --violet: #7567f7;
  --mint: #19b99a;
  --orange: #e68145;
  --red: #df5b70;
  --navy: #202840;
  --shadow: 0 18px 45px rgba(30, 40, 80, .09);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; overflow-x: hidden; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 16px/1.65 Manrope, Arial, sans-serif; overflow-x: hidden; }
button, input { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
main { width: min(1320px, calc(100% - 48px)); margin: 0 auto; padding: 28px 0 80px; }
.site-header { min-height: 76px; }
.eyebrow { margin: 0 0 13px; color: var(--indigo); font: 500 12px/1.3 'DM Mono', monospace; letter-spacing: 1.15px; }
.lead { color: #56627a; font-size: 19px; line-height: 1.72; }
.button { display: inline-flex; align-items: center; justify-content: center; min-height: 45px; padding: 11px 18px; border: 1px solid var(--indigo); border-radius: 9px; background: var(--indigo); color: #fff; font-size: 14px; font-weight: 800; text-decoration: none; cursor: pointer; transition: transform .18s ease, background .18s ease, box-shadow .18s ease; }
.button:hover { transform: translateY(-2px); background: #3f37cf; box-shadow: 0 10px 22px rgba(78, 70, 229, .18); }
.button.outline { background: #fff; color: var(--indigo); border-color: #c9c7ef; }
.button.outline:hover { background: #f0efff; }
.button.disabled { border-color: #4b556f; background: #39425a; color: #9fa8bc; cursor: default; box-shadow: none; transform: none; }
.lesson-section { margin-top: 86px; scroll-margin-top: 100px; }
.lesson-head { max-width: 960px; margin-bottom: 28px; }
.lesson-head h2 { margin: 0 0 12px; font-size: clamp(34px, 4vw, 52px); line-height: 1.14; letter-spacing: -1.8px; }
.lesson-head > p:last-child:not(.eyebrow) { margin: 0; color: var(--muted); font-size: 18px; }
.site-footer { padding: 28px 24px; border-top: 1px solid var(--line); color: #7b879d; text-align: center; font-size: 13px; }
.site-footer p { margin: 0; }

@media (max-width: 760px) {
  body { font-size: 15px; }
  main { width: min(100% - 32px, 1320px); padding-top: 18px; }
  .lead { font-size: 17px; }
  .lesson-section { margin-top: 64px; }
  .lesson-head h2 { font-size: 32px; letter-spacing: -1px; }
  .lesson-head > p:last-child:not(.eyebrow) { font-size: 16px; }
}