/* ============ Heizi Tech — light, clean, education style ============ */
:root {
  --bg: #ffffff;
  --bg-alt: #f6f9fd;
  --text: #16233a;
  --muted: #5d6f89;
  --line: #e6ecf5;
  --blue: #2563eb;
  --blue-dark: #1d4ed8;
  --blue-soft: #e8f0fe;
  --green: #10b981;
  --green-soft: #dcf7ec;
  --amber: #f59e0b;
  --amber-soft: #fef3d9;
  --violet: #8b5cf6;
  --violet-soft: #ece7fd;
  --radius: 18px;
  --shadow: 0 12px 40px rgba(22, 35, 58, 0.08);
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, "Helvetica Neue", Arial, sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
.container { max-width: 1120px; margin: 0 auto; padding: 0 24px; }
img { max-width: 100%; }

/* ---------- buttons / links ---------- */
.btn {
  display: inline-block;
  padding: 13px 28px;
  border-radius: 999px;
  font-weight: 600;
  font-size: 15px;
  text-decoration: none;
  transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
}
.btn-primary { background: var(--blue); color: #fff; box-shadow: 0 6px 20px rgba(37, 99, 235, 0.35); }
.btn-primary:hover { background: var(--blue-dark); transform: translateY(-2px); }
.btn-ghost { background: #fff; color: var(--text); border: 1.5px solid var(--line); }
.btn-ghost:hover { border-color: var(--blue); color: var(--blue); }
.btn-white { background: #fff; color: var(--blue-dark); }
.btn-white:hover { transform: translateY(-2px); box-shadow: 0 10px 24px rgba(0,0,0,0.15); }
.btn-sm { padding: 10px 22px; font-size: 14px; }

/* ---------- nav ---------- */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255, 255, 255, 0.88);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}
.nav-inner { display: flex; align-items: center; justify-content: space-between; height: 68px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--text); }
.brand-mark {
  width: 34px; height: 34px; border-radius: 10px;
  background: linear-gradient(135deg, var(--blue), #60a5fa);
  color: #fff; font-weight: 800; font-size: 18px;
  display: flex; align-items: center; justify-content: center;
}
.brand-name { font-weight: 700; font-size: 17px; }
.nav-links { display: flex; gap: 28px; }
.nav-links a { text-decoration: none; color: var(--muted); font-weight: 500; font-size: 15px; }
.nav-links a:hover { color: var(--blue); }

/* ---------- hero ---------- */
.hero {
  padding: 96px 0 88px;
  background:
    radial-gradient(600px 300px at 12% 8%, #e8f0fe 0%, transparent 60%),
    radial-gradient(520px 280px at 88% 20%, #dcf7ec 0%, transparent 60%),
    var(--bg);
}
.hero-grid { display: grid; grid-template-columns: 1.05fr 0.95fr; gap: 56px; align-items: center; }
.badge {
  display: inline-block; padding: 7px 16px; border-radius: 999px;
  background: var(--blue-soft); color: var(--blue-dark);
  font-size: 13px; font-weight: 600; margin-bottom: 20px;
}
.hero h1 { font-size: 52px; line-height: 1.14; letter-spacing: -1.5px; font-weight: 800; }
.hero h1 em { font-style: normal; color: var(--blue); }
.lead { font-size: 18px; color: var(--muted); margin: 20px 0 32px; max-width: 480px; }
.hero-actions { display: flex; gap: 14px; flex-wrap: wrap; }
.hero-proof { display: flex; align-items: center; gap: 14px; margin-top: 36px; }
.avatars { display: flex; }
.avatars span {
  width: 36px; height: 36px; border-radius: 50%;
  background: linear-gradient(135deg, #93c5fd, #60a5fa);
  color: #fff; font-size: 13px; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  border: 2.5px solid #fff; margin-left: -10px;
}
.avatars span:first-child { margin-left: 0; }
.avatars span:nth-child(2) { background: linear-gradient(135deg, #6ee7b7, #34d399); }
.avatars span:nth-child(3) { background: linear-gradient(135deg, #fcd34d, #fbbf24); }
.avatars span:nth-child(4) { background: var(--text); }
.hero-proof p { font-size: 14px; color: var(--muted); }

/* hero mock cards */
.hero-visual { position: relative; height: 460px; }
.mock-card {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 18px; position: absolute;
}
.chat-card { width: 340px; top: 8px; left: 24px; z-index: 2; }
.mock-header { display: flex; align-items: center; gap: 6px; margin-bottom: 14px; }
.dot { width: 10px; height: 10px; border-radius: 50%; background: #e2e8f0; }
.dot:first-child { background: #f87171; } .dot:nth-child(2) { background: #fbbf24; } .dot:nth-child(3) { background: #34d399; }
.mock-title { margin-left: 6px; font-size: 13px; font-weight: 600; color: var(--muted); }
.chat-row { display: flex; margin-bottom: 10px; }
.chat-row.user { justify-content: flex-end; }
.bubble {
  max-width: 82%; padding: 10px 14px; border-radius: 14px; font-size: 13.5px; line-height: 1.5;
}
.chat-row.bot .bubble { background: var(--bg-alt); border-bottom-left-radius: 4px; }
.chat-row.user .bubble { background: var(--blue); color: #fff; border-bottom-right-radius: 4px; }
.typing { display: flex; gap: 5px; padding: 4px 2px; }
.typing span { width: 7px; height: 7px; border-radius: 50%; background: #c3cede; animation: blink 1.2s infinite; }
.typing span:nth-child(2) { animation-delay: 0.2s; } .typing span:nth-child(3) { animation-delay: 0.4s; }
@keyframes blink { 0%, 100% { opacity: 0.3; } 50% { opacity: 1; } }
.streak-card { width: 210px; bottom: 24px; right: 8px; text-align: center; z-index: 3; }
.streak-num { font-size: 44px; font-weight: 800; color: var(--text); }
.streak-label { font-size: 14px; color: var(--muted); margin-bottom: 12px; }
.progress { height: 8px; background: var(--line); border-radius: 99px; overflow: hidden; margin-bottom: 8px; }
.progress-bar { width: 85%; height: 100%; border-radius: 99px; background: linear-gradient(90deg, var(--green), #34d399); }
.streak-sub { font-size: 12px; color: var(--muted); }

/* ---------- sections ---------- */
.section { padding: 88px 0; }
.section-alt { background: var(--bg-alt); }
.eyebrow {
  color: var(--blue); font-weight: 700; font-size: 13px;
  text-transform: uppercase; letter-spacing: 1.5px; margin-bottom: 12px;
}
.section h2 { font-size: 36px; letter-spacing: -0.8px; font-weight: 800; }
.section-sub { color: var(--muted); font-size: 17px; margin: 12px auto 0; max-width: 560px; }
.section > .container { text-align: center; }

/* ---------- features ---------- */
.feature-grid {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px;
  margin-top: 48px; text-align: left;
}
.card {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 28px 24px; transition: transform 0.18s ease, box-shadow 0.18s ease;
}
.section-alt .card { border-color: transparent; box-shadow: var(--shadow); }
.card:hover { transform: translateY(-5px); box-shadow: var(--shadow); }
.icon {
  width: 48px; height: 48px; border-radius: 14px;
  display: flex; align-items: center; justify-content: center; margin-bottom: 18px;
}
.icon svg { width: 24px; height: 24px; }
.icon-blue { background: var(--blue-soft); color: var(--blue); }
.icon-green { background: var(--green-soft); color: var(--green); }
.icon-amber { background: var(--amber-soft); color: var(--amber); }
.icon-violet { background: var(--violet-soft); color: var(--violet); }
.card h3 { font-size: 17px; margin-bottom: 8px; }
.card p { font-size: 14.5px; color: var(--muted); }

/* ---------- steps ---------- */
.steps { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; margin-top: 48px; text-align: left; }
.step {
  background: #fff; border-radius: var(--radius); padding: 32px 28px;
  box-shadow: var(--shadow); position: relative;
}
.step-num {
  width: 44px; height: 44px; border-radius: 50%;
  background: var(--blue); color: #fff; font-weight: 800; font-size: 18px;
  display: flex; align-items: center; justify-content: center; margin-bottom: 18px;
}
.step h3 { font-size: 18px; margin-bottom: 8px; }
.step p { font-size: 14.5px; color: var(--muted); }

/* ---------- about ---------- */
.about-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 56px; text-align: left; align-items: start; }
.values { display: flex; flex-direction: column; gap: 14px; }
.value {
  background: var(--bg-alt); border-radius: 14px; padding: 18px 20px;
  display: flex; flex-direction: column; gap: 4px;
}
.value strong { font-size: 15.5px; }
.value span { font-size: 14px; color: var(--muted); }

/* ---------- cta ---------- */
.cta { padding: 24px 0 88px; background: var(--bg); }
.cta-box {
  background: linear-gradient(135deg, #2563eb, #4f46e5);
  border-radius: 26px; padding: 64px 48px; text-align: center; color: #fff;
  box-shadow: 0 20px 60px rgba(37, 99, 235, 0.35);
}
.cta-box h2 { font-size: 34px; letter-spacing: -0.6px; margin-bottom: 12px; }
.cta-box p { opacity: 0.9; margin-bottom: 28px; font-size: 16.5px; }

/* ---------- contact ---------- */
.contact-box .email-link {
  display: inline-block; margin-top: 24px; font-size: 24px; font-weight: 700;
  color: var(--blue); text-decoration: none; border-bottom: 2px solid var(--blue-soft);
}
.contact-box .email-link:hover { border-color: var(--blue); }

/* ---------- footer ---------- */
.footer { border-top: 1px solid var(--line); padding: 28px 0; }
.footer-inner { display: flex; align-items: center; justify-content: space-between; }
.footer p { font-size: 13.5px; color: var(--muted); }

/* ---------- responsive ---------- */
@media (max-width: 900px) {
  .hero-grid { grid-template-columns: 1fr; }
  .hero h1 { font-size: 38px; }
  .hero { padding: 64px 0; }
  .hero-visual { height: 420px; max-width: 480px; margin: 0 auto; width: 100%; }
  .feature-grid { grid-template-columns: repeat(2, 1fr); }
  .steps { grid-template-columns: 1fr; }
  .about-grid { grid-template-columns: 1fr; }
  .nav-links { display: none; }
  .cta-box { padding: 48px 28px; }
}
@media (max-width: 560px) {
  .feature-grid { grid-template-columns: 1fr; }
  .hero h1 { font-size: 32px; }
  .chat-card { width: 300px; left: 0; }
}