/* ═══════════════ GRAVITY PLAYGROUND ═══════════════ */
:root{
  --bg:#070b18;
  --bg2:#0b1226;
  --panel:rgba(18,26,48,.72);
  --panel-brd:rgba(120,160,255,.14);
  --ink:#e8eeff;
  --muted:#8ea0c8;
  --dim:#63739a;
  --a:#4cc9ff;      /* cyan  - body A */
  --b:#ff7ad9;      /* pink  - body B */
  --acc:#7c5cff;    /* violet */
  --ok:#3ddc97;
  --warn:#ffcf5c;
  --danger:#ff6b6b;
  --r:16px;
  --shadow:0 20px 50px rgba(0,0,0,.45);
  font-synthesis-weight:none;
}
*{box-sizing:border-box}
html,body{height:100%}
html{background:var(--bg)}
body{
  margin:0;
  background:
    radial-gradient(1100px 700px at 15% -10%, #1b2a5c 0%, transparent 60%),
    radial-gradient(900px 600px at 105% 10%, #3a1b5c 0%, transparent 60%),
    linear-gradient(180deg,var(--bg2),var(--bg) 60%);
  background-attachment:fixed;
  color:var(--ink);
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Inter,Roboto,system-ui,sans-serif;
  -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
}
.hidden{display:none !important}
button{font-family:inherit;cursor:pointer}
h1,h2,h3,h4{margin:0}

/* ─────────── HOME ─────────── */
.home{position:fixed;inset:0;display:grid;place-items:center;z-index:50;overflow:hidden;
  animation:fadeIn .5s ease}
.stars{position:absolute;inset:0;width:100%;height:100%}
.home-inner{position:relative;text-align:center;padding:28px;max-width:820px}
.home-badge{display:inline-block;font-size:11px;letter-spacing:.28em;color:#9fb4ff;
  border:1px solid rgba(140,170,255,.3);padding:6px 14px;border-radius:99px;background:rgba(90,120,255,.08);margin-bottom:22px}
.home-title{font-size:clamp(34px,7.5vw,74px);font-weight:800;letter-spacing:-.02em;line-height:1.05;
  background:linear-gradient(90deg,#fff,#a9c7ff 55%,#c8a6ff);-webkit-background-clip:text;background-clip:text;color:transparent}
.home-title .thin{font-weight:200;letter-spacing:.02em}
.home-title .planet{color:#fff;-webkit-text-fill-color:#fff;filter:drop-shadow(0 0 22px rgba(80,160,255,.65));display:inline-block;
  animation:float 5s ease-in-out infinite}
.home-sub{color:var(--muted);font-size:clamp(14px,2.4vw,19px);margin:16px 0 30px;font-style:italic}
.btn.btn-hero{font-size:16px;font-weight:800;letter-spacing:.14em;padding:17px 42px;border-radius:99px;
  background:linear-gradient(135deg,var(--acc),#2b8bff);border:none;color:#fff;
  box-shadow:0 0 0 1px rgba(255,255,255,.16) inset, 0 14px 40px rgba(90,80,255,.45);
  transition:transform .18s ease, box-shadow .18s ease}
.btn.btn-hero:hover{transform:translateY(-2px) scale(1.02);box-shadow:0 0 0 1px rgba(255,255,255,.25) inset,0 18px 52px rgba(90,80,255,.6)}
.home-chips{display:flex;gap:8px;justify-content:center;flex-wrap:wrap;margin-top:26px}
.chip{font-size:12px;color:#b9c9ef;background:rgba(255,255,255,.05);border:1px solid rgba(255,255,255,.09);
  padding:6px 12px;border-radius:99px}
.home-feats{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:10px;margin-top:34px}
.home-feats>div{background:rgba(255,255,255,.035);border:1px solid rgba(255,255,255,.07);border-radius:12px;padding:12px 10px;text-align:left}
.home-feats b{display:block;font-size:13px}
.home-feats span{display:block;font-size:11.5px;color:var(--dim);margin-top:3px}
@keyframes float{0%,100%{transform:translateY(0)}50%{transform:translateY(-12px)}}
@keyframes fadeIn{from{opacity:0}to{opacity:1}}

/* ─────────── APP SHELL ─────────── */
.app{min-height:100vh;display:flex;flex-direction:column;animation:fadeIn .4s ease}
.topbar{display:flex;align-items:center;gap:16px;padding:12px 18px;
  border-bottom:1px solid var(--panel-brd);background:rgba(9,14,30,.6);backdrop-filter:blur(14px);
  position:sticky;top:0;z-index:20;flex-wrap:wrap}
.brand{font-size:14px;letter-spacing:.14em;color:#cbd8f7;cursor:pointer;white-space:nowrap}
.brand b{font-weight:800;color:#fff}
.modes{display:flex;gap:6px;background:rgba(255,255,255,.05);padding:4px;border-radius:99px;margin:0 auto}
.mode-tab{border:none;background:transparent;color:var(--muted);font-size:12px;font-weight:700;letter-spacing:.1em;
  padding:9px 16px;border-radius:99px;transition:.18s}
.mode-tab:hover{color:#fff}
.mode-tab.active{background:linear-gradient(135deg,var(--acc),#2b8bff);color:#fff;box-shadow:0 6px 18px rgba(90,80,255,.4)}
.topbar-right{display:flex;align-items:center;gap:10px}
.tag{font-size:11px;letter-spacing:.16em;color:var(--ok);border:1px solid rgba(61,220,151,.35);
  background:rgba(61,220,151,.1);padding:6px 12px;border-radius:99px;white-space:nowrap}
.tag.running{color:var(--warn);border-color:rgba(255,207,92,.4);background:rgba(255,207,92,.1)}
.tag.paused{color:#9fb4ff;border-color:rgba(140,170,255,.4);background:rgba(140,170,255,.1)}

.layout{display:grid;grid-template-columns:300px minmax(0,1fr) 340px;gap:14px;padding:14px;align-items:start;flex:1}

/* ─────────── PANELS / CARDS ─────────── */
.panel,.card{background:var(--panel);border:1px solid var(--panel-brd);border-radius:var(--r);
  box-shadow:var(--shadow);backdrop-filter:blur(12px)}
.panel{padding:16px}
.panel-title{font-size:11px;letter-spacing:.24em;color:var(--dim);margin-bottom:14px}
.side{background:none;border:none;box-shadow:none;padding:0;display:flex;flex-direction:column;gap:12px}
.card{padding:14px}
.card-head{display:flex;align-items:center;justify-content:space-between;gap:8px;margin-bottom:10px}
.card-head h3{font-size:11px;letter-spacing:.2em;color:var(--dim)}
.mini{background:none;border:none;color:var(--dim);font-size:10.5px;text-decoration:underline;opacity:.75}
.mini:hover{color:var(--ink)}

/* ─────────── CONTROLS ─────────── */
.ctrl{margin-bottom:18px}
.ctrl-head{display:flex;align-items:center;justify-content:space-between;gap:8px;margin-bottom:8px}
.ctrl-head label{font-size:11px;letter-spacing:.12em;color:#b7c6ea;font-weight:700;display:flex;align-items:center;gap:6px}
.ctrl-head.sub label{font-size:10px;color:var(--dim);letter-spacing:.1em}
.ctrl-head output{font-size:13px;font-weight:800;color:#fff;font-variant-numeric:tabular-nums;
  background:rgba(255,255,255,.06);padding:3px 9px;border-radius:8px}
.dot{width:9px;height:9px;border-radius:50%;display:inline-block}
.dot-a{background:var(--a);box-shadow:0 0 10px var(--a)}
.dot-b{background:var(--b);box-shadow:0 0 10px var(--b)}
.hint{font-size:11px;color:var(--dim);margin-top:7px;line-height:1.5}
.hint b{color:#b7c6ea}

input[type=range]{-webkit-appearance:none;appearance:none;width:100%;height:5px;border-radius:99px;
  background:linear-gradient(90deg,var(--acc) var(--fill,50%),rgba(255,255,255,.12) var(--fill,50%));outline:none}
input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;width:18px;height:18px;border-radius:50%;
  background:#fff;border:3px solid var(--acc);cursor:grab;box-shadow:0 0 14px rgba(124,92,255,.7);transition:transform .12s}
input[type=range]::-webkit-slider-thumb:active{transform:scale(1.18);cursor:grabbing}
input[type=range]::-moz-range-thumb{width:16px;height:16px;border-radius:50%;background:#fff;border:3px solid var(--acc);cursor:grab}
input[type=range]:disabled{opacity:.4}
#gravityA{--c:var(--a)}
.presets{display:grid;grid-template-columns:1fr 1fr;gap:6px;margin-top:10px}
.presets button{font-size:11px;padding:7px 6px;border-radius:9px;border:1px solid rgba(255,255,255,.1);
  background:rgba(255,255,255,.04);color:#c3d0ee;transition:.15s;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.presets button:hover{background:rgba(124,92,255,.22);border-color:rgba(124,92,255,.55);color:#fff}
.presets button.on{background:rgba(124,92,255,.3);border-color:var(--acc);color:#fff}

.switch{position:relative;display:inline-block;width:44px;height:24px}
.switch input{opacity:0;width:0;height:0}
.slider-sw{position:absolute;inset:0;background:rgba(255,255,255,.14);border-radius:99px;transition:.2s}
.slider-sw:before{content:"";position:absolute;width:18px;height:18px;left:3px;top:3px;background:#fff;border-radius:50%;transition:.2s}
.switch input:checked+.slider-sw{background:linear-gradient(135deg,var(--acc),#2b8bff)}
.switch input:checked+.slider-sw:before{transform:translateX(20px)}
.air-block{transition:opacity .2s}
.air-block.disabled{opacity:.4}
.check{display:flex;align-items:center;gap:9px;font-size:12px;color:#b7c6ea;cursor:pointer}
.check input{width:16px;height:16px;accent-color:var(--acc)}

/* ─────────── STAGE ─────────── */
.stage{display:flex;flex-direction:column;gap:12px;min-width:0}
.readouts{display:grid;gap:10px;grid-template-columns:repeat(auto-fit,minmax(120px,1fr))}
.ro{background:var(--panel);border:1px solid var(--panel-brd);border-radius:14px;padding:11px 13px;box-shadow:var(--shadow)}
.ro-label{font-size:9.5px;letter-spacing:.18em;color:var(--dim);margin-bottom:5px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.ro-val{font-size:clamp(19px,2.4vw,27px);font-weight:800;font-variant-numeric:tabular-nums;line-height:1;letter-spacing:-.02em}
.ro-unit{font-size:12px;color:var(--dim);font-weight:600;margin-left:3px}
.ro.a .ro-val{color:var(--a);text-shadow:0 0 22px rgba(76,201,255,.4)}
.ro.b .ro-val{color:var(--b);text-shadow:0 0 22px rgba(255,122,217,.4)}
.ro-group{grid-column:1/-1;display:grid;gap:10px;grid-template-columns:repeat(auto-fit,minmax(110px,1fr))}
.ro-title{grid-column:1/-1;font-size:10px;letter-spacing:.2em;color:var(--muted);display:flex;align-items:center;gap:7px;margin-top:2px}

.canvas-wrap{position:relative;border-radius:var(--r);overflow:hidden;border:1px solid var(--panel-brd);
  background:linear-gradient(180deg,#080d1e,#0d1430 60%,#101a3a);box-shadow:var(--shadow);
  /* explicit height: the canvas fills it, so its size never feeds back into layout */
  height:clamp(340px,62vh,660px)}
#sim{display:block;width:100%;height:100%}
.gindicator{position:absolute;top:12px;left:12px;display:flex;align-items:baseline;gap:5px;
  background:rgba(8,12,28,.7);border:1px solid rgba(124,92,255,.35);border-radius:12px;padding:8px 12px;backdrop-filter:blur(8px)}
.gi-arrow{color:var(--acc);font-size:17px;animation:bob 1.4s ease-in-out infinite;text-shadow:0 0 12px var(--acc)}
.gi-val{font-size:17px;font-weight:800;font-variant-numeric:tabular-nums}
.gi-unit{font-size:10px;color:var(--dim)}
@keyframes bob{0%,100%{transform:translateY(-2px);opacity:.65}50%{transform:translateY(3px);opacity:1}}

.toast{position:absolute;left:50%;top:22px;transform:translate(-50%,-24px);opacity:0;pointer-events:none;
  background:linear-gradient(135deg,rgba(61,220,151,.95),rgba(43,139,255,.95));color:#04121a;font-weight:800;
  font-size:13px;letter-spacing:.08em;padding:11px 20px;border-radius:99px;box-shadow:0 12px 34px rgba(0,0,0,.5);
  transition:.35s cubic-bezier(.2,1.4,.4,1);white-space:nowrap;max-width:92%;overflow:hidden;text-overflow:ellipsis}
.toast.show{opacity:1;transform:translate(-50%,0)}

.buttons{display:grid;grid-template-columns:1.4fr 1fr 1fr 1fr;gap:9px}
.btn{border:1px solid rgba(255,255,255,.12);background:rgba(255,255,255,.06);color:var(--ink);
  font-size:13px;font-weight:800;letter-spacing:.09em;padding:14px 10px;border-radius:13px;transition:.16s}
.btn:hover{background:rgba(255,255,255,.13);transform:translateY(-1px)}
.btn:active{transform:translateY(0)}
.btn-primary{background:linear-gradient(135deg,var(--acc),#2b8bff);border-color:transparent;
  box-shadow:0 10px 26px rgba(90,80,255,.35)}
.btn-primary:hover{box-shadow:0 12px 32px rgba(90,80,255,.55);background:linear-gradient(135deg,#8f72ff,#3f9bff)}
.btn-ghost{background:transparent;color:var(--muted)}

/* ─────────── GRAPH ─────────── */
#graph{width:100%;height:170px;display:block;border-radius:10px;background:rgba(4,8,20,.5)}
.seg{display:flex;background:rgba(255,255,255,.05);border-radius:9px;padding:3px}
.seg button{border:none;background:transparent;color:var(--dim);font-size:10.5px;font-weight:700;padding:5px 9px;border-radius:7px}
.seg button.active{background:rgba(124,92,255,.35);color:#fff}
.legend{display:flex;gap:14px;flex-wrap:wrap;margin-top:8px;font-size:11px;color:var(--muted)}
.legend i{width:10px;height:10px;border-radius:3px;display:inline-block;margin-right:5px;vertical-align:-1px}

/* ─────────── RESULTS ─────────── */
.results-empty{font-size:12px;color:var(--dim);line-height:1.6}
.res-title{font-size:12px;font-weight:800;letter-spacing:.16em;color:var(--ok);margin-bottom:10px}
.res-grid{display:grid;grid-template-columns:1fr 1fr;gap:8px}
.res-item{background:rgba(255,255,255,.045);border-radius:10px;padding:9px 11px}
.res-item .k{font-size:9.5px;letter-spacing:.14em;color:var(--dim)}
.res-item .v{font-size:17px;font-weight:800;font-variant-numeric:tabular-nums;margin-top:3px}
.res-sub{font-size:11px;letter-spacing:.14em;color:var(--muted);margin:12px 0 6px;font-weight:700}
.res-why{font-size:12px;line-height:1.65;color:#c2cfec}
.res-why b{color:#fff}
.res-badge{display:inline-block;font-size:10px;font-weight:800;letter-spacing:.1em;padding:4px 9px;border-radius:99px;margin-bottom:8px}
.badge-a{background:rgba(76,201,255,.16);color:var(--a);border:1px solid rgba(76,201,255,.35)}
.badge-b{background:rgba(255,122,217,.16);color:var(--b);border:1px solid rgba(255,122,217,.35)}
.badge-tie{background:rgba(61,220,151,.16);color:var(--ok);border:1px solid rgba(61,220,151,.35)}

#eduBody h4{font-size:12px;letter-spacing:.16em;color:var(--warn);margin-bottom:7px}
#eduBody p{font-size:12.5px;line-height:1.65;color:#c2cfec;margin:0}
#eduBody p+p{margin-top:8px}
#eduBody code{background:rgba(255,255,255,.08);padding:1px 5px;border-radius:5px;font-size:11.5px}

/* ─────────── CHALLENGES ─────────── */
.chal{display:flex;gap:10px;align-items:flex-start;padding:9px 10px;border-radius:11px;cursor:pointer;
  border:1px solid transparent;transition:.15s;margin-bottom:5px}
.chal:hover{background:rgba(255,255,255,.05)}
.chal.active{background:rgba(124,92,255,.14);border-color:rgba(124,92,255,.45)}
.chal.done .chal-t{color:var(--ok)}
.chal-mark{width:19px;height:19px;border-radius:6px;border:1.5px solid rgba(255,255,255,.2);flex:none;
  display:grid;place-items:center;font-size:11px;color:var(--ok);margin-top:1px}
.chal.done .chal-mark{border-color:var(--ok);background:rgba(61,220,151,.16)}
.chal-t{font-size:12px;font-weight:700;line-height:1.35}
.chal-d{font-size:10.5px;color:var(--dim);margin-top:3px;line-height:1.45}
.chal-best{font-size:10px;color:var(--warn);margin-top:3px}
.predict{margin-top:10px;padding:11px;border-radius:11px;background:rgba(124,92,255,.1);border:1px solid rgba(124,92,255,.3)}
.predict-q{font-size:11.5px;font-weight:700;margin-bottom:8px}
.predict-btns{display:flex;gap:6px}
.predict-btns button{flex:1;font-size:11px;font-weight:700;padding:8px 4px;border-radius:8px;
  border:1px solid rgba(255,255,255,.14);background:rgba(255,255,255,.05);color:#c3d0ee}
.predict-btns button.on{background:var(--acc);border-color:var(--acc);color:#fff}
.predict-status{font-size:11px;color:var(--muted);margin-top:8px;min-height:14px}

/* ─────────── RESPONSIVE ─────────── */
@media (max-width:1180px){
  .layout{grid-template-columns:280px minmax(0,1fr);}
  .side{grid-column:1/-1;display:grid;grid-template-columns:1fr 1fr;align-items:start}
}
@media (max-width:860px){
  .layout{grid-template-columns:1fr;padding:10px;gap:10px}
  .side{grid-template-columns:1fr}
  .stage{order:-1}
  .canvas-wrap{height:min(56vh,430px)}
  .modes{width:100%;order:3;margin:0;justify-content:center}
  .mode-tab{flex:1;padding:9px 6px;font-size:10.5px;letter-spacing:.06em}
  .topbar{padding:10px 12px;gap:10px}
  .buttons{grid-template-columns:1fr 1fr;position:sticky;bottom:0;z-index:10;
    background:rgba(9,14,30,.85);backdrop-filter:blur(10px);padding:8px;margin:0 -4px -4px;border-radius:14px}
  .readouts{grid-template-columns:repeat(auto-fit,minmax(96px,1fr));gap:7px}
  .ro{padding:9px 10px}
  .presets{grid-template-columns:1fr 1fr}
}
@media (max-width:400px){
  .readouts{grid-template-columns:1fr 1fr}
}