:root{
  --bg:#0f1724;
  --panel:#0b1220;
  --accent:#10b981;
  --btn:#111827;
  --btn-hover:#1f2937;
  --text:#e6eef8;
  --muted:#94a3b8;
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family:Inter, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
  background:linear-gradient(180deg,#071024 0%, #0b1220 100%);
  color:var(--text);
  display:flex;
  align-items:center;
  justify-content:center;
  padding:24px;
}

.app{width:320px; max-width:96%}

.calculator{
  background:linear-gradient(180deg, rgba(255,255,255,0.02), rgba(255,255,255,0.01));
  border-radius:12px;
  padding:18px;
  box-shadow: 0 10px 30px rgba(2,6,23,0.6), inset 0 1px 0 rgba(255,255,255,0.02);
}

.display{
  height:64px;
  background:linear-gradient(180deg, rgba(255,255,255,0.01), rgba(0,0,0,0.2));
  border-radius:8px;
  padding:12px;
  font-size:28px;
  display:flex;
  align-items:center;
  justify-content:flex-end;
  overflow:hidden;
  color:var(--text);
  margin-bottom:12px;
  word-break:break-all;
}

.keys{
  display:grid;
  grid-template-columns: repeat(4,1fr);
  gap:10px;
}

.btn{
  background:var(--btn);
  color:var(--text);
  border:0;
  padding:16px;
  border-radius:8px;
  font-size:18px;
  cursor:pointer;
  transition:all .12s ease;
  box-shadow: 0 4px 10px rgba(2,6,23,0.5);
}

.btn:active{transform:translateY(1px)}
.btn:hover{background:var(--btn-hover)}

.btn.operator{background:transparent; border:1px solid rgba(255,255,255,0.04)}
.btn.equals{
  grid-row: span 2;
  background:linear-gradient(180deg,var(--accent), #059669);
  color:white;
  font-weight:600;
  font-size:22px;
  box-shadow: 0 8px 18px rgba(16,185,129,0.18);
}
.btn.zero{grid-column: span 2}

.function{background:rgba(255,255,255,0.03)}
.hint{margin-top:10px;color:var(--muted);font-size:13px;text-align:center}

.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}