:root{
  --bg: #0d1117;
  --bg-elev: #161b22;
  --text: #e6edf3;
  --muted: #8b949e;
  --accent: #2f81f7;
  --accent-press: #1f6feb;
  --key-bg: #21262d;
  --key-op: #2d333b;
  --key-eq: #238636;
  --key-eq-press: #1a7f37;
  --danger: #f85149;
  color-scheme: dark light;
}
@media (prefers-color-scheme: light){
  :root{
    --bg:#f6f8fa;
    --bg-elev:#ffffff;
    --text:#24292f;
    --muted:#57606a;
    --accent:#0969da;
    --accent-press:#0759b8;
    --key-bg:#eaeef2;
    --key-op:#dde3ea;
    --key-eq:#2da44e;
    --key-eq-press:#2c974b;
    --danger:#cf222e;
  }
}
:root[data-theme="light"]{
  --bg:#f6f8fa;
  --bg-elev:#ffffff;
  --text:#24292f;
  --muted:#57606a;
  --accent:#0969da;
  --accent-press:#0759b8;
  --key-bg:#eaeef2;
  --key-op:#dde3ea;
  --key-eq:#2da44e;
  --key-eq-press:#2c974b;
  --danger:#cf222e;
}
*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji","Segoe UI Emoji";
  background:var(--bg);
  color:var(--text);
  display:flex;
  flex-direction:column;
  min-height:100vh;
}
.sr-only{
  position:absolute;
  width:1px;height:1px;
  padding:0;margin:-1px;
  overflow:hidden;clip:rect(0,0,0,0);
  border:0;
}
.app-header, .app-footer{
  display:flex;
  align-items:center;
  justify-content:space-between;
  padding:12px 16px;
  background:var(--bg-elev);
  border-bottom:1px solid rgba(127,127,127,.15);
}
.app-footer{
  border-top:1px solid rgba(127,127,127,.15);
  border-bottom:none;
  justify-content:center;
}
.brand{
  font-weight:600;
}
.toggles{display:flex; gap:8px}
.btn{
  border:1px solid rgba(127,127,127,.25);
  background:transparent;
  color:var(--text);
  padding:6px 10px;
  border-radius:8px;
  cursor:pointer;
}
.btn.ghost:hover{background:rgba(127,127,127,.12)}
main{
  flex:1;
  display:grid;
  place-items:center;
  padding:12px;
}
.calculator{
  width:100%;
  max-width:420px;
  background:var(--bg-elev);
  border:1px solid rgba(127,127,127,.15);
  border-radius:16px;
  padding:12px;
  box-shadow: 0 4px 20px rgba(0,0,0,.15);
}
.display{
  background:var(--bg);
  border-radius:12px;
  padding:12px 12px;
  display:flex;
  flex-direction:column;
  align-items:flex-end;
  min-height:88px;
  gap:6px;
  border:1px solid rgba(127,127,127,.12);
}
.display-prev{
  color:var(--muted);
  min-height:20px;
  font-size:14px;
}
.display-curr{
  font-variant-numeric: tabular-nums;
  font-size:36px;
  line-height:1;
  word-break:break-all;
  max-width:100%;
}
.keys{
  margin-top:12px;
  display:grid;
  grid-template-columns: repeat(4, 1fr);
  gap:8px;
}
.key{
  background:var(--key-bg);
  color:var(--text);
  border:none;
  padding:16px;
  border-radius:12px;
  font-size:18px;
  cursor:pointer;
  user-select:none;
  touch-action:manipulation;
  transition:transform .02s ease, background .12s ease;
}
.key:active{ transform:scale(0.98) }
.key.fn{ background: var(--key-op); }
.key.op{ background: var(--accent); }
.key.op:active{ background: var(--accent-press); }
.key.eq{ background: var(--key-eq); }
.key.eq:active{ background: var(--key-eq-press); }
.key.zero{
  grid-column: span 2;
}
.key:focus-visible{
  outline:2px solid var(--accent);
  outline-offset:2px;
}
small{color:var(--muted)}
@media (min-width:700px){
  .display-curr{font-size:44px}
  .key{font-size:20px; padding:18px}
}