:root{
  --bg:#12161d;
  --surface:#1b212b;
  --surface-hi:#232a36;
  --line:#2c3442;
  --ink:#eceef1;
  --ink-mute:#8a93a6;
  --amber:#f2b134;
  --teal:#4fd1c5;
  --radius:14px;
}
:root[data-theme="light"]{
  --bg:#f4f5f7;
  --surface:#ffffff;
  --surface-hi:#eceef2;
  --line:#dde1e7;
  --ink:#20242c;
  --ink-mute:#666e7d;
  --amber:#c8790f;
  --teal:#1f8f83;
}
*{box-sizing:border-box;}
html,body{margin:0;padding:0;}
body{
  background:
    radial-gradient(circle at 15% 0%, rgba(242,177,52,0.06), transparent 40%),
    radial-gradient(circle at 85% 100%, rgba(79,209,197,0.06), transparent 40%),
    var(--bg);
  color:var(--ink);
  font-family:'Inter',sans-serif;
  min-height:100vh;
  padding:48px 20px 80px;
  transition:background-color .25s ease, color .25s ease;
}
.wrap{max-width:720px;margin:0 auto;}

/* Site-wide top bar */
.site-bar{
  max-width:1040px;
  margin:0 auto;
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:20px;
  padding:0 20px 40px;
  flex-wrap:wrap;
}
.brand{
  display:flex;
  align-items:center;
  gap:10px;
  text-decoration:none;
  color:var(--ink);
}
.brand-logo{
  width:30px;height:30px;
  border-radius:7px;
  background:#0c0f14;
  color:var(--teal);
  display:flex;
  align-items:center;
  justify-content:center;
  font-family:'Space Grotesk',sans-serif;
  font-weight:700;
  font-size:16px;
  flex-shrink:0;
}
.brand-name{
  font-family:'Space Grotesk',sans-serif;
  font-weight:700;
  font-size:16px;
  letter-spacing:-0.01em;
}
.bar-right{
  display:flex;
  align-items:center;
  gap:22px;
  flex-wrap:wrap;
}
.site-nav{
  display:flex;
  gap:22px;
}
.site-nav a{
  color:var(--ink-mute);
  text-decoration:none;
  font-size:14px;
  font-weight:500;
  transition:color .15s ease;
}
.site-nav a:hover{color:var(--ink);}
.site-nav a.active{color:var(--amber);}

.theme-toggle{
  display:flex;
  align-items:center;
  gap:6px;
  background:var(--surface);
  border:1px solid var(--line);
  border-radius:999px;
  padding:4px;
  flex-shrink:0;
}
.theme-btn{
  border:none;
  background:transparent;
  color:var(--ink-mute);
  font-family:'JetBrains Mono',monospace;
  font-size:12px;
  padding:7px 13px;
  border-radius:999px;
  cursor:pointer;
  display:flex;
  align-items:center;
  gap:6px;
  transition:background .15s ease, color .15s ease;
}
.theme-btn:hover{color:var(--ink);}
.theme-btn.active{
  background:var(--surface-hi);
  color:var(--ink);
  box-shadow:inset 0 0 0 1px var(--line);
}
.theme-btn svg{width:13px;height:13px;}

header{margin-bottom:36px;}
.eyebrow{
  font-family:'JetBrains Mono',monospace;
  font-size:12px;
  letter-spacing:0.14em;
  text-transform:uppercase;
  color:var(--amber);
  display:flex;
  align-items:center;
  gap:8px;
  margin-bottom:14px;
}
.eyebrow::before{
  content:"";
  width:20px;height:1px;
  background:var(--amber);
  display:inline-block;
}
h1{
  font-family:'Space Grotesk',sans-serif;
  font-size:clamp(30px,5vw,42px);
  font-weight:700;
  margin:0 0 8px;
  letter-spacing:-0.01em;
}
.sub{color:var(--ink-mute);font-size:15px;line-height:1.5;max-width:52ch;}

/* Tabs */
.tabs{
  display:flex;
  gap:6px;
  background:var(--surface);
  border:1px solid var(--line);
  border-radius:12px;
  padding:5px;
  margin-bottom:28px;
}
.tab{
  flex:1;
  text-align:center;
  padding:11px 8px;
  border-radius:8px;
  font-size:13.5px;
  font-weight:500;
  color:var(--ink-mute);
  cursor:pointer;
  border:none;
  background:transparent;
  font-family:'Inter',sans-serif;
  transition:background .15s ease, color .15s ease;
}
.tab:hover{color:var(--ink);}
.tab.active{
  background:var(--surface-hi);
  color:var(--ink);
  box-shadow:inset 0 0 0 1px var(--line);
}

/* Panels */
.panel{display:none;}
.panel.active{display:block; animation: fade .25s ease;}
@keyframes fade{from{opacity:0; transform:translateY(4px);} to{opacity:1; transform:translateY(0);}}

.card{
  background:var(--surface);
  border:1px solid var(--line);
  border-radius:var(--radius);
  padding:28px;
  transition:background-color .25s ease, border-color .25s ease;
}

.equation{
  display:flex;
  align-items:center;
  flex-wrap:wrap;
  gap:10px;
  font-family:'Space Grotesk',sans-serif;
  font-size:18px;
  color:var(--ink-mute);
  margin-bottom:26px;
  line-height:1.6;
}
.equation .word{color:var(--ink);}
input.field{
  width:110px;
  background:var(--surface-hi);
  border:1px solid var(--line);
  border-radius:8px;
  color:var(--ink);
  font-family:'JetBrains Mono',monospace;
  font-size:16px;
  font-weight:500;
  padding:9px 10px;
  text-align:center;
  outline:none;
  transition:border-color .15s ease;
}
input.field:focus{border-color:var(--amber);}
input.field::placeholder{color:#4a5468;}

.result-row{
  display:flex;
  align-items:baseline;
  justify-content:space-between;
  padding-top:22px;
  border-top:1px dashed var(--line);
}
.result-label{
  font-size:12.5px;
  text-transform:uppercase;
  letter-spacing:0.08em;
  color:var(--ink-mute);
  font-family:'JetBrains Mono',monospace;
}
.result-value{
  font-family:'Space Grotesk',sans-serif;
  font-size:34px;
  font-weight:700;
  color:var(--amber);
}
.result-value .unit{font-size:20px;color:var(--ink-mute);font-weight:500;margin-left:2px;}

/* Signature: proportion bar */
.bar-wrap{margin-top:20px;}
.bar-track{
  position:relative;
  height:10px;
  border-radius:6px;
  background:var(--surface-hi);
  border:1px solid var(--line);
  overflow:hidden;
}
.bar-fill{
  position:absolute;
  top:0;left:0;bottom:0;
  width:0%;
  background:linear-gradient(90deg,var(--teal),var(--amber));
  border-radius:6px;
  transition:width .4s cubic-bezier(.4,0,.2,1);
}
.bar-labels{
  display:flex;
  justify-content:space-between;
  margin-top:8px;
  font-family:'JetBrains Mono',monospace;
  font-size:11.5px;
  color:var(--ink-mute);
}

/* Explanation box */
.explain{
  margin-top:20px;
  background:var(--surface-hi);
  border:1px solid var(--line);
  border-left:3px solid var(--teal);
  border-radius:10px;
  padding:16px 18px;
}
.explain-label{
  font-size:11px;
  text-transform:uppercase;
  letter-spacing:0.09em;
  color:var(--teal);
  font-family:'JetBrains Mono',monospace;
  margin-bottom:8px;
  display:block;
}
.explain-text{
  font-size:14px;
  line-height:1.65;
  color:var(--ink-mute);
}
.explain-text strong{
  color:var(--ink);
  font-weight:600;
  font-family:'JetBrains Mono',monospace;
}

footer{
  margin-top:40px;
  text-align:center;
  font-size:12.5px;
  color:var(--ink-mute);
  font-family:'JetBrains Mono',monospace;
}
footer a{color:var(--ink-mute); text-decoration:underline; transition:color .15s ease;}
footer a:hover{color:var(--ink);}

@media (max-width:480px){
  .equation{font-size:16px;}
  input.field{width:90px;}
  .result-value{font-size:28px;}
  .site-bar{justify-content:center; text-align:center;}
  .bar-right{justify-content:center; width:100%;}
}