:root {
  /* Brand palette, taken from the logo. Keep favicon.svg and README in sync. */
  --navy: #2f3f95;        /* beret: primary actions, links, headings accents */
  --navy-dark: #1f2a66;   /* hover, concept bar */
  --mint: #bfe3d6;        /* logo badge: highlight surfaces */
  --mint-soft: #e8f5ef;   /* tutor bubbles, soft panels */
  --fur: #fbf0d9;         /* logo fur: warm panels */
  --peach: #f4d3b3;       /* muzzle: step numbers, borders */
  --blush: #f6b6a7;       /* inner ear: decorative accents only */
  --coral: #c2564a;       /* blush darkened for small accent text (AA on cream) */
  --cream: #fffaf2;       /* page background */
  --ink: #2b2522;         /* logo outline: body text */
  --muted: #6b5f57;
  --card: #ffffff;
  --line: #eadfd2;
  --radius: 18px;
  font-family: "Inter", "PingFang SC", "Noto Sans SC", system-ui, -apple-system, "Segoe UI", sans-serif;
  color: var(--ink);
  background: var(--cream);
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
body { margin: 0; line-height: 1.6; }
a { color: var(--navy); }
img { max-width: 100%; }

.concept-bar { background: var(--navy-dark); color: #fff; text-align: center; font-size: .85rem; padding: .45rem 1rem; }

.nav { position: sticky; top: 0; z-index: 10; display: flex; align-items: center; gap: 1.5rem; padding: .8rem clamp(1rem, 4vw, 3rem); background: rgba(255, 248, 239, .92); backdrop-filter: blur(8px); border-bottom: 1px solid var(--line); }
.brand { display: flex; align-items: center; gap: .5rem; font-weight: 800; font-size: 1.25rem; color: var(--ink); text-decoration: none; }
.links { display: flex; gap: 1.25rem; flex: 1; }
.links a { color: var(--muted); text-decoration: none; font-weight: 500; }
.links a:hover { color: var(--navy); }
.actions { display: flex; align-items: center; gap: 1rem; margin-left: auto; }
.lang-switch { display: inline-flex; border: 1px solid var(--line); border-radius: 999px; overflow: hidden; background: #fff; }
.lang-switch button { border: 0; background: transparent; padding: .35rem .8rem; cursor: pointer; font: inherit; font-size: .9rem; color: var(--muted); }
.lang-switch button[aria-pressed="true"] { background: var(--navy); color: #fff; }

.hero { display: grid; grid-template-columns: 1.2fr 1fr; gap: 3rem; align-items: center; max-width: 1150px; margin: 0 auto; padding: clamp(2.5rem, 7vw, 5.5rem) clamp(1rem, 4vw, 3rem); }
.eyebrow { color: var(--coral); font-weight: 700; text-transform: uppercase; letter-spacing: .08em; font-size: .85rem; margin: 0 0 .6rem; }
h1 { font-size: clamp(2rem, 4.4vw, 3.3rem); line-height: 1.15; margin: 0 0 1.2rem; letter-spacing: -.02em; }
.lead { font-size: 1.12rem; color: var(--muted); margin: 0 0 1.8rem; }
.cta { display: flex; flex-wrap: wrap; gap: .8rem; align-items: center; }
.fine { font-size: .82rem; color: var(--muted); margin-top: .9rem; }
.btn { display: inline-flex; align-items: center; gap: .6rem; padding: .75rem 1.3rem; border-radius: 999px; border: 1px solid var(--navy); background: var(--navy); color: #fff; font: inherit; font-weight: 600; text-decoration: none; cursor: pointer; }
.btn.ghost { background: transparent; color: var(--navy); }
.btn:hover { filter: brightness(1.05); transform: translateY(-1px); }

.hero-art { position: relative; display: grid; place-items: center; }
.hero-art img { width: min(320px, 70vw); filter: drop-shadow(0 18px 30px rgba(43, 37, 34, .16)); animation: bob 4s ease-in-out infinite; }
.bubble { position: absolute; background: #fff; border: 1px solid var(--line); border-radius: 16px; padding: .55rem .9rem; font-size: .92rem; box-shadow: 0 8px 20px rgba(0, 0, 0, .06); }
.b1 { top: 6%; right: 0; border-bottom-left-radius: 4px; }
.b2 { bottom: 6%; left: 0; border-top-right-radius: 4px; background: var(--mint-soft); }
@keyframes bob { 50% { transform: translateY(-8px); } }

.stats { display: grid; grid-template-columns: repeat(3, 1fr); max-width: 1000px; margin: 0 auto 2rem; padding: 0 1rem; gap: 1rem; text-align: center; }
.stats div { background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 1.2rem; }
.stats strong { display: block; font-size: 2rem; color: var(--navy); }
.stats span { color: var(--muted); font-size: .92rem; }

.section { padding: clamp(3rem, 7vw, 5rem) clamp(1rem, 4vw, 3rem); max-width: 1150px; margin: 0 auto; }
.section.alt { max-width: none; background: #fff; }
.section.alt > * { max-width: 1050px; margin-left: auto; margin-right: auto; }
h2 { font-size: clamp(1.6rem, 3vw, 2.3rem); margin: 0 0 1rem; text-align: center; letter-spacing: -.01em; }
.sub { text-align: center; color: var(--muted); margin: -.3rem auto 2rem; }
.grid3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.2rem; margin-top: 2rem; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.5rem; }
.card h3 { margin: 0 0 .5rem; font-size: 1.1rem; }
.card p { margin: 0; color: var(--muted); }

.steps { list-style: none; padding: 0; display: grid; grid-template-columns: repeat(4, 1fr); gap: 1.2rem; margin-top: 2rem; }
.steps li { background: var(--cream); border-radius: var(--radius); padding: 1.4rem; }
.steps h3 { margin: .6rem 0 .4rem; font-size: 1.05rem; }
.steps p { margin: 0; color: var(--muted); font-size: .95rem; }
.num { display: inline-grid; place-items: center; width: 2.1rem; height: 2.1rem; border-radius: 50%; background: var(--mint); color: var(--ink); font-weight: 800; }

.demo { display: grid; grid-template-columns: 2fr 1fr; gap: 1.2rem; }
.chat { background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 1.4rem; display: flex; flex-direction: column; gap: .8rem; }
.msg { max-width: 85%; padding: .75rem 1rem; border-radius: 14px; }
.msg b { display: block; font-size: .78rem; text-transform: uppercase; letter-spacing: .05em; opacity: .7; }
.msg.tutor { background: var(--mint-soft); align-self: flex-start; }
.msg.me { background: var(--navy); color: #fff; align-self: flex-end; }
.msg.note { background: var(--fur); border-left: 4px solid var(--peach); align-self: stretch; max-width: none; }
.score { background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 1.4rem; }
.score h3 { margin-top: 0; }
.bar { margin: .9rem 0; }
.bar span { font-size: .9rem; color: var(--muted); }
.bar i { display: block; height: 10px; border-radius: 99px; background: linear-gradient(90deg, var(--navy) var(--v), var(--line) var(--v)); margin-top: .3rem; }

.chips { list-style: none; padding: 0; display: flex; flex-wrap: wrap; justify-content: center; gap: .9rem; }
.chips li { background: var(--cream); border: 1px solid var(--line); border-radius: 999px; padding: .7rem 1.3rem; font-size: 1.15rem; font-weight: 600; }
.chips small { display: block; font-size: .75rem; color: var(--muted); font-weight: 400; text-align: center; }

.timeline { list-style: none; padding: 0; display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.2rem; counter-reset: s; }
.timeline li { border-top: 4px solid var(--mint); padding-top: 1rem; }
.timeline li::before { counter-increment: s; content: "Phase " counter(s); display: block; font-size: .8rem; color: var(--coral); font-weight: 700; }
html[lang="zh-CN"] .timeline li::before { content: "阶段 " counter(s); }
.timeline b { display: block; font-size: 1.1rem; }
.timeline span { color: var(--muted); }

.signup { text-align: center; }
.signup p { color: var(--muted); }
.signup .btn { margin: 1rem auto 0; justify-content: center; }

.footer { text-align: center; padding: 2rem 1rem 3rem; color: var(--muted); font-size: .9rem; border-top: 1px solid var(--line); }


@media (max-width: 860px) {
  .links { display: none; }
  .hero { grid-template-columns: 1fr; text-align: center; }
  .hero .cta { justify-content: center; }
  .grid3, .steps, .timeline, .demo, .stats { grid-template-columns: 1fr; }
}
@media (prefers-reduced-motion: reduce) { .hero-art img { animation: none; } }

.beta-form { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; max-width: 620px; margin: 2rem auto 0; text-align: left; background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 1.6rem; }
.beta-form label { display: flex; flex-direction: column; gap: .35rem; font-size: .9rem; font-weight: 600; }
.beta-form input, .beta-form select { font: inherit; font-weight: 400; padding: .65rem .8rem; border: 1px solid var(--line); border-radius: 10px; background: var(--cream); }
.beta-form input:focus, .beta-form select:focus { outline: 2px solid var(--navy); outline-offset: 1px; }
.beta-form .wide { grid-column: 1 / -1; }
.beta-form .check { flex-direction: row; align-items: flex-start; gap: .6rem; font-weight: 400; color: var(--muted); }
.beta-form .check input { margin-top: .3rem; }
.beta-form .btn { justify-content: center; margin: 0; }
.beta-form .btn:disabled { opacity: .6; cursor: wait; }
.form-status { margin: 0; min-height: 1.2em; font-size: .92rem; }
.form-status[data-kind="ok"] { color: #1d7a46; font-weight: 600; }
.form-status[data-kind="error"] { color: #b3261e; }
@media (max-width: 860px) { .beta-form { grid-template-columns: 1fr; } }
.hp { position: absolute; left: -9999px; width: 1px; height: 1px; opacity: 0; }