/* ============================================================
   小白兔TKNC — 基础重置 + 版式骨架 + 导航 + 页脚 + 页面区块标题
   ============================================================ */

*{box-sizing:border-box;margin:0;padding:0;-webkit-tap-highlight-color:transparent}
html{-webkit-text-size-adjust:100%}
body{
  font-family:var(--sans);
  background:var(--bg);
  color:var(--ink);
  line-height:1.55;
  letter-spacing:.01em;
  -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
}
/* faint instrument grain + top glow behind hero */
body::before{
  content:"";position:fixed;inset:0;z-index:0;pointer-events:none;
  background:
    radial-gradient(120% 60% at 50% -8%, rgba(52,227,176,.10), transparent 60%),
    radial-gradient(90% 50% at 85% 0%, rgba(55,182,255,.07), transparent 55%);
}
.wrap{position:relative;z-index:1;max-width:var(--maxw);margin:0 auto;padding:0 18px}
h1,h2,h3{letter-spacing:-.02em;line-height:1.12}
.mono{font-family:var(--mono);font-feature-settings:"tnum" 1,"zero" 1}
a{color:inherit;text-decoration:none}
button{font-family:inherit;cursor:pointer;border:none;background:none;color:inherit}
img{max-width:100%;display:block}
[hidden]{display:none !important}

/* ============================== NAV ============================== */
.nav{
  position:sticky;top:0;z-index:40;
  backdrop-filter:saturate(160%) blur(14px);
  background:rgba(11,12,16,.72);
  border-bottom:1px solid var(--line);
}
.nav-in{max-width:var(--maxw);margin:0 auto;padding:12px 18px;display:flex;align-items:center;justify-content:space-between}
.brand{display:flex;align-items:center;gap:9px;font-weight:700;font-size:15.5px}
.brand .dot{
  width:26px;height:26px;border-radius:8px;display:grid;place-items:center;font-size:15px;
  background:var(--acc-grad);box-shadow:0 4px 14px rgba(52,227,176,.28);
}
.brand small{color:var(--ink-3);font-weight:500;font-size:11px;letter-spacing:.08em;margin-left:2px}
.nav a.gh{display:flex;align-items:center;gap:6px;color:var(--ink-2);font-size:13px;padding:6px 10px;border:1px solid var(--line);border-radius:999px}
.nav a.gh:hover{color:var(--ink);border-color:var(--line-2)}

/* ============================== SECTIONS (信号/原理/FAQ) ============================== */
.section{padding:34px 0 6px}
.sec-h{font-size:11px;letter-spacing:.16em;text-transform:uppercase;color:var(--acc);font-weight:600;margin-bottom:6px;display:flex;align-items:center;gap:8px}
.sec-h::before{content:"";width:18px;height:1px;background:var(--acc)}
.sec-t{font-size:22px;font-weight:750;margin-bottom:18px;letter-spacing:-.02em}

.grid6{display:grid;grid-template-columns:repeat(2,1fr);gap:10px}
.sig{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:15px 14px;transition:border-color .18s,transform .18s}
.sig:hover{border-color:var(--line-2);transform:translateY(-2px)}
.sig .si{font-size:22px;margin-bottom:9px}
.sig h4{font-size:14px;font-weight:650;margin-bottom:4px}
.sig p{font-size:12px;color:var(--ink-3);line-height:1.5}
.sig .w{font-size:10px;font-family:var(--mono);color:var(--ink-4);margin-top:8px;letter-spacing:.04em}

/* principle */
.principles{display:flex;flex-direction:column;gap:11px}
.prin{display:flex;gap:14px;background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:16px}
.prin-n{font-family:var(--mono);font-size:24px;font-weight:700;color:var(--surface-3);flex-shrink:0;line-height:1;
        -webkit-text-stroke:1px var(--line-2)}
.prin h4{font-size:15px;font-weight:650;margin-bottom:4px}
.prin p{font-size:12.5px;color:var(--ink-3);line-height:1.55}
.prin p b{color:var(--ink-2)}
.prin-lead{color:var(--ink-2);font-size:13.5px;margin-bottom:16px;line-height:1.6}
.prin-lead b{color:var(--ink)}

/* faq */
.faq-item{border-bottom:1px solid var(--line)}
.faq-q{width:100%;text-align:left;padding:15px 2px;font-size:14.5px;font-weight:550;display:flex;justify-content:space-between;align-items:center;gap:12px}
.faq-q .fc{color:var(--ink-4);transition:transform .22s;flex-shrink:0}
.faq-item.open .fc{transform:rotate(45deg)}
.faq-a{max-height:0;overflow:hidden;transition:max-height .28s ease;color:var(--ink-3);font-size:13px;line-height:1.65}
.faq-item.open .faq-a{max-height:360px}
.faq-a .inner{padding:0 2px 15px}

/* ============================== FOOTER ============================== */
.footer{margin-top:40px;border-top:1px solid var(--line);padding:26px 0 44px;text-align:center}
.foot-priv{font-size:11.5px;color:var(--ink-4);line-height:1.7;max-width:520px;margin:0 auto 16px}
.foot-priv b{color:var(--ink-2)}
.built-row{display:flex;justify-content:center;margin:6px 0 2px}
.built{
  display:inline-flex;align-items:center;gap:8px;font-size:12px;color:var(--ink-2);
  padding:7px 14px;border:1px solid var(--line);border-radius:999px;
}
.built .spark{width:16px;height:16px;border-radius:5px;background:var(--acc-grad);display:grid;place-items:center;font-size:10px}
.built b{background:var(--acc-grad);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent;font-weight:700}
.foot-links{margin-top:14px;display:flex;gap:16px;justify-content:center;font-size:12px;color:var(--ink-3)}
.foot-links a:hover{color:var(--ink)}

/* ============================== RESPONSIVE ============================== */
@media(max-width:380px){
  .grid6{gap:8px}
}
@media(min-width:560px){
  .grid6{grid-template-columns:repeat(3,1fr)}
}