:root { --bg:#0F172A; --bg2:#1E293B; --border:#2D3F55; --accent:#7C3AED; --accent2:#A78BFA; --text:#F1F5F9; --text2:#94A3B8; --text3:#64748B; --key:#27364b; --key-hover:#31435b; --op:#3b2a6e; --op-hover:#4a3688; --danger:#F87171; --ok:#10B981; }
@media (prefers-color-scheme: light) {
  :root { --bg:#F1F5F9; --bg2:#FFFFFF; --border:#CBD5E1; --accent:#7C3AED; --accent2:#6D28D9; --text:#0F172A; --text2:#475569; --text3:#64748B; --key:#E2E8F0; --key-hover:#CBD5E1; --op:#EDE9FE; --op-hover:#DDD6FE; --danger:#DC2626; --ok:#059669; }
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: system-ui, -apple-system, 'Segoe UI', Roboto, 'Noto Sans Bengali', sans-serif; background: var(--bg); color: var(--text); line-height: 1.5; min-height: 100vh; display: flex; flex-direction: column; }
a { color: inherit; }
.wrap { width: 100%; max-width: 1080px; margin: 0 auto; padding: 0 16px; }
header { border-bottom: 1px solid var(--border); background: var(--bg2); }
header .wrap { display: flex; align-items: center; justify-content: space-between; height: 60px; gap: 12px; }
.logo { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 1.25rem; letter-spacing: -0.02em; text-decoration: none; }
.logo-mark { width: 30px; height: 30px; border-radius: 8px; background: linear-gradient(135deg, var(--accent), #A78BFA); display: grid; place-items: center; font-size: 16px; color: #fff; }
.logo small { font-weight: 500; font-size: 0.72rem; color: var(--text3); letter-spacing: 0.04em; }
.lang { border: 1px solid var(--border); background: transparent; color: var(--text); border-radius: 8px; padding: 6px 12px; font: inherit; font-size: 0.85rem; cursor: pointer; }
.lang:hover { border-color: var(--accent); }
main { flex: 1; padding: 24px 0 40px; }
h1 { font-size: clamp(1.4rem, 4vw, 2rem); letter-spacing: -0.02em; text-align: center; }
.sub { text-align: center; color: var(--text2); margin: 6px auto 20px; max-width: 560px; font-size: 0.95rem; }
.calc { margin: 0 auto; width: 100%; max-width: 400px; background: var(--bg2); border: 1px solid var(--border); border-radius: 18px; padding: 14px; }
.calc.sci { max-width: 760px; }
.screen { background: var(--bg); border: 1px solid var(--border); border-radius: 12px; padding: 10px 14px; min-height: 96px; display: flex; flex-direction: column; justify-content: flex-end; text-align: right; overflow: hidden; }
.screen .meta { display: flex; justify-content: space-between; font-size: 0.75rem; color: var(--text3); min-height: 1.1em; }
.screen .expr { font-size: 1.05rem; color: var(--text2); word-break: break-all; min-height: 1.6em; font-variant-numeric: tabular-nums; }
.screen .res { font-size: 2.2rem; font-weight: 600; word-break: break-all; line-height: 1.2; font-variant-numeric: tabular-nums; }
.screen .res.mid { font-size: 1.7rem; }
.screen .res.small { font-size: 1.2rem; }
.screen .res.err { color: var(--danger); font-size: 1.1rem; }
.pads { display: grid; gap: 12px; margin-top: 12px; }
.pad { display: grid; gap: 8px; }
.pad.main { grid-template-columns: repeat(4, 1fr); }
.pad.sci { grid-template-columns: repeat(5, 1fr); }
@media (min-width: 720px) { .calc.sci .pads { grid-template-columns: 1.15fr 1fr; align-items: start; } }
button.k { font: inherit; font-size: 1.15rem; min-height: 52px; border: 0; border-radius: 12px; background: var(--key); color: var(--text); cursor: pointer; touch-action: manipulation; transition: background .1s; }
button.k:hover { background: var(--key-hover); }
button.k:active { transform: scale(.97); }
button.k:focus-visible, .lang:focus-visible, summary:focus-visible { outline: 2px solid var(--accent2); outline-offset: 2px; }
button.k.op { background: var(--op); color: var(--accent2); }
button.k.op:hover { background: var(--op-hover); }
button.k.eq { background: var(--accent); color: #fff; }
button.k.eq:hover { filter: brightness(1.1); }
button.k.fn { font-size: .95rem; min-height: 44px; }
button.k.on { outline: 2px solid var(--accent2); }
button.k.span2 { grid-column: span 2; }
.history { margin-top: 12px; border-top: 1px solid var(--border); padding-top: 8px; }
.history summary { cursor: pointer; font-size: .9rem; color: var(--text2); padding: 4px 0; }
.history ul { list-style: none; max-height: 200px; overflow: auto; margin-top: 6px; }
.history li button { width: 100%; text-align: right; background: transparent; border: 0; color: var(--text); font: inherit; font-size: .9rem; padding: 6px 4px; border-radius: 8px; cursor: pointer; }
.history li button:hover { background: var(--key); }
.history li small { display: block; color: var(--text3); }
.history .empty { color: var(--text3); font-size: .85rem; padding: 6px 0; }
.history .clear { margin-top: 6px; font: inherit; font-size: .8rem; background: transparent; color: var(--text2); border: 1px solid var(--border); border-radius: 8px; padding: 4px 10px; cursor: pointer; }
.info { max-width: 720px; margin: 36px auto 0; color: var(--text2); font-size: .95rem; }
.info h2 { color: var(--text); font-size: 1.1rem; margin: 18px 0 6px; }
.info ul { padding-left: 20px; }
.info a { color: var(--accent2); }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
footer { border-top: 1px solid var(--border); padding: 20px 0; color: var(--text3); font-size: 0.85rem; text-align: center; }
footer a { text-decoration: underline; }