:root {
  /* page */
  --bg: #f3f1ec;
  --grid: rgba(40, 60, 90, 0.06);
  --card: #fffefb;
  --ink: #171a1f;
  --muted: #5d6470;
  --line: #e1ddd3;
  --chip: #edeae2;
  --accent: #d9481f;
  --shadow: 0 1px 2px rgba(23, 26, 31, 0.06), 0 12px 32px -12px rgba(23, 26, 31, 0.18);

  /* the calculator body looks the same in light and dark */
  --d-body: #1d2128;
  --d-edge: #2b313b;
  --d-key: #353c48;
  --d-key-lo: #23282f;
  --d-fn: #272c35;
  --d-op: #3b4a66;
  --d-ink: #f1f3f6;
  --d-dim: #8b95a5;
  --d-accent: #ff6a3d;
  --lcd: #dfe6da;
  --lcd-lo: #cdd6c7;
  --lcd-ink: #151a14;
  --lcd-dim: #5c6858;

  --mono: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, "Roboto Mono", monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0e1116;
    --grid: rgba(140, 170, 220, 0.05);
    --card: #161a21;
    --ink: #eceff3;
    --muted: #98a2b1;
    --line: #272d37;
    --chip: #20252e;
    --accent: #ff7a4f;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 16px 40px -16px rgba(0, 0, 0, 0.7);
    --d-body: #1a1e25;
    --d-edge: #333a46;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  color: var(--ink);
  background-color: var(--bg);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 24px 24px;
  font: 16px/1.55 var(--sans);
  -webkit-text-size-adjust: 100%;
}

.top, .app, .doc, .foot {
  max-width: 1000px;
  margin: 0 auto;
  padding: 0 16px;
}

/* header */
.top {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px 28px;
  padding-top: 22px;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  text-decoration: none;
  font-size: 1.45rem;
  font-weight: 750;
  letter-spacing: -0.03em;
}
.brand svg { display: block; border-radius: 9px; }
.intro { flex: 1 1 320px; }
h1 { margin: 0; font-size: 1.05rem; font-weight: 650; line-height: 1.3; letter-spacing: -0.01em; }
.intro p { margin: 2px 0 0; color: var(--muted); font-size: 0.9rem; }

.app {
  display: grid;
  gap: 20px;
  margin-top: 20px;
  grid-template-columns: minmax(0, 1fr);
}
@media (min-width: 860px) {
  .app { grid-template-columns: minmax(0, 470px) minmax(0, 1fr); align-items: start; }
}

/* ---- the calculator ---- */
.device {
  padding: 14px;
  color: var(--d-ink);
  background: linear-gradient(180deg, var(--d-edge), var(--d-body) 90px);
  border: 1px solid var(--d-edge);
  border-radius: 24px;
  box-shadow: var(--shadow), inset 0 1px 0 rgba(255, 255, 255, 0.07);
}

.device-top {
  display: flex;
  align-items: center;
  gap: 10px;
  min-height: 30px;
  padding: 0 6px 10px;
}
.etch { font-size: 0.7rem; font-weight: 700; letter-spacing: 0.22em; color: var(--d-ink); }
.etch.dim { margin-left: auto; letter-spacing: 0.14em; font-weight: 600; color: var(--d-accent); }
.kb {
  width: 40px;
  height: 30px;
  font-size: 1rem;
  color: var(--d-ink);
  background: var(--d-fn);
  border: 1px solid var(--d-edge);
  border-radius: 8px;
  cursor: pointer;
}
.kb[aria-pressed="true"] { border-color: var(--d-accent); color: var(--d-accent); }

/* display */
.lcd {
  padding: 12px 14px 10px;
  color: var(--lcd-ink);
  background: linear-gradient(180deg, var(--lcd-lo), var(--lcd) 14px);
  border-radius: 14px;
  box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.28), 0 1px 0 rgba(255, 255, 255, 0.08);
}

.field {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 3px 0 3px 8px;
  border-left: 3px solid transparent;
  border-bottom: 1px dashed rgba(21, 26, 20, 0.16);
  cursor: text;
}
.field.on { border-left-color: var(--accent); }
.fl {
  flex: 0 0 6.6em;
  white-space: nowrap;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--lcd-dim);
}
.field input {
  flex: 1;
  min-width: 0;
  padding: 6px 0;
  font: 600 1.15rem/1.2 var(--mono);
  color: var(--lcd-ink);
  background: none;
  border: 0;
  border-radius: 0;
  outline: none;
}
.field input::placeholder { color: var(--lcd-dim); opacity: 0.5; font-weight: 500; }
/* a value the solver worked out, shown where you would have typed it */
.field input.computed::placeholder { color: #9c2f0d; opacity: 1; font-weight: 700; }
.fields.solo .field { padding-left: 8px; }
.fields.solo input { font-size: 1.3rem; padding: 8px 0; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

.readout { padding: 8px 0 0 11px; min-height: 92px; }
.kind { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.12em; text-transform: uppercase; color: var(--lcd-dim); }
.result {
  font: 700 2rem/1.15 var(--mono);
  letter-spacing: -0.03em;
  overflow-wrap: anywhere;
}
.result.long { font-size: 1.5rem; }
.result.idle { opacity: 0.28; }
.note { margin-top: 2px; font-size: 0.8rem; line-height: 1.35; color: var(--lcd-dim); min-height: 1.35em; }
.note.bad { color: #a11d0a; font-weight: 600; }

/* function keys */
.modes {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 6px;
  margin: 12px 0 10px;
}
.modes a {
  display: flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  height: 36px;
  padding: 0 4px;
  font: 650 0.78rem/1 var(--sans);
  letter-spacing: 0.03em;
  white-space: nowrap;
  color: var(--d-dim);
  background: var(--d-fn);
  border: 1px solid var(--d-edge);
  border-radius: 9px;
  cursor: pointer;
  touch-action: manipulation;
}
.modes a:hover { color: var(--d-ink); }
.modes a[aria-current="page"] {
  color: var(--d-accent);
  border-color: var(--d-accent);
  background: rgba(255, 106, 61, 0.1);
}
@media (min-width: 460px) {
  .modes { grid-template-columns: repeat(6, 1fr); }
}

/* keypad */
.keypad { display: grid; grid-template-columns: repeat(5, 1fr); gap: 8px; }

.keypad button {
  height: 54px;
  padding: 0;
  font: 550 1.3rem/1 var(--sans);
  white-space: nowrap;
  color: var(--d-ink);
  background: var(--d-key);
  border: 0;
  border-radius: 12px;
  box-shadow: 0 3px 0 var(--d-key-lo), inset 0 1px 0 rgba(255, 255, 255, 0.09);
  cursor: pointer;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  user-select: none;
  transition: transform 40ms, box-shadow 40ms;
}
.keypad button:active { transform: translateY(2px); box-shadow: 0 1px 0 var(--d-key-lo); }
.keypad .fn { background: var(--d-fn); color: var(--d-dim); font-size: 1.05rem; }
.keypad .sm { font-size: 0.78rem; font-weight: 650; letter-spacing: 0.04em; }
/* space separates whole inches from the fraction, so it should not look like a minor key */
.keypad [data-k=" "] { background: var(--d-key); color: var(--d-ink); box-shadow: 0 3px 0 var(--d-key-lo), inset 0 0 0 1px rgba(255, 106, 61, 0.55); }
.keypad .clr { color: var(--d-accent); font-weight: 700; }
.keypad .op { background: var(--d-op); font-size: 1.55rem; font-weight: 400; }
.keypad .unit { background: var(--d-fn); font-size: 0.72rem; font-weight: 650; letter-spacing: 0.04em; color: var(--d-dim); }
.keypad .unit b { font: 700 1.3rem/1 var(--mono); color: var(--d-ink); margin-left: 3px; vertical-align: -3px; }
.keypad .eq { background: var(--d-accent); color: #1d0d06; font-size: 1.6rem; font-weight: 700; box-shadow: 0 3px 0 #a53a18, inset 0 1px 0 rgba(255, 255, 255, 0.3); }
.keypad .eq:active { box-shadow: 0 1px 0 #a53a18; }

button:focus-visible, select:focus-visible, a:focus-visible {
  outline: 2px solid var(--d-accent);
  outline-offset: 2px;
}

/* ---- results sheet ---- */
.sheet {
  padding: 18px 20px 20px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 18px;
  box-shadow: var(--shadow);
}
.row.head { display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.sheet h2 { margin: 0; font-size: 0.74rem; font-weight: 700; letter-spacing: 0.12em; text-transform: uppercase; color: var(--muted); }
.prec { font-size: 0.85rem; color: var(--muted); white-space: nowrap; }
.prec select {
  margin-left: 4px;
  padding: 6px 8px;
  font: inherit;
  color: var(--ink);
  background: var(--chip);
  border: 1px solid var(--line);
  border-radius: 8px;
}

.alts, .tape { list-style: none; margin: 12px 0 0; padding: 0; }
.alts li {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 10px 0;
  border-top: 1px solid var(--line);
}
.alts .label { flex: 0 0 9.5em; font-size: 0.85rem; color: var(--muted); }
.alts .val { flex: 1; min-width: 0; font: 650 1.05rem/1.3 var(--mono); letter-spacing: -0.01em; overflow-wrap: anywhere; }

.mem { margin-top: 26px; }
.mem-val { margin-top: 10px; padding-top: 10px; border-top: 1px solid var(--line); font: 700 1.3rem/1.3 var(--mono); color: var(--accent); overflow-wrap: anywhere; }
.mem-note { margin: 4px 0 0; font-size: 0.82rem; color: var(--muted); }
.mem-note:empty { display: none; }
.copy, .link {
  font: 600 0.78rem var(--sans);
  color: var(--muted);
  background: none;
  border: 0;
  padding: 4px;
  cursor: pointer;
}
.copy:hover, .link:hover { color: var(--accent); }
.empty { margin: 12px 0 0; padding-top: 12px; border-top: 1px solid var(--line); font-size: 0.9rem; color: var(--muted); }

#tape-wrap { margin-top: 26px; }
.tape li { border-top: 1px solid var(--line); }
.tape button {
  display: block;
  width: 100%;
  padding: 9px 0;
  text-align: left;
  font: 0.88rem/1.35 var(--mono);
  color: var(--muted);
  background: none;
  border: 0;
  cursor: pointer;
  overflow-wrap: anywhere;
}
.tape button b { color: var(--ink); }
.tape button:hover b { color: var(--accent); }

/* ---- article ---- */
.doc { margin-top: 44px; }
.doc h2 {
  margin: 36px 0 8px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
  font-size: 1.3rem;
  letter-spacing: -0.02em;
}
.doc h3 { margin: 20px 0 2px; font-size: 1rem; }
.doc p { margin: 0 0 8px; max-width: 70ch; }
.doc code, .doc kbd {
  font: 0.9em var(--mono);
  background: var(--chip);
  padding: 1px 5px;
  border-radius: 5px;
}
.examples { list-style: none; margin: 14px 0 0; padding: 0; display: grid; gap: 8px; }
@media (min-width: 700px) { .examples { grid-template-columns: 1fr 1fr; } }
.examples li { display: flex; flex-wrap: wrap; align-items: center; gap: 4px 10px; }
.examples button {
  font: 650 0.92rem/1 var(--mono);
  color: var(--ink);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 9px 10px;
  cursor: pointer;
}
.examples button:hover { border-color: var(--accent); color: var(--accent); }
.examples span { font-size: 0.85rem; color: var(--muted); }
.try {
  padding: 9px 12px;
  font: 650 0.9rem/1.3 var(--sans);
  color: var(--accent);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
}
.try:hover { border-color: var(--accent); }
.more { list-style: none; margin: 12px 0 0; padding: 0; display: grid; gap: 10px; }
@media (min-width: 700px) { .more { grid-template-columns: 1fr 1fr; } }
.more li { padding: 12px 14px; background: var(--card); border: 1px solid var(--line); border-radius: 12px; }
.more a { display: block; font-weight: 650; color: var(--accent); text-decoration: none; }
.more a:hover { text-decoration: underline; }
.more span { font-size: 0.88rem; color: var(--muted); }
.plain { margin: 14px 0 0; padding-left: 20px; max-width: 70ch; }
.plain li { margin-bottom: 4px; }

.cards { display: grid; gap: 12px; margin-top: 14px; }
@media (min-width: 700px) { .cards { grid-template-columns: repeat(2, 1fr); } }
.cards section {
  padding: 14px 16px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
}
.cards h3 { margin: 0 0 4px; }
.cards a { color: var(--accent); text-decoration: none; }
.cards a:hover { text-decoration: underline; }
.cards p { margin: 0; font-size: 0.93rem; color: var(--muted); }
.cards button {
  margin-top: 10px;
  padding: 8px 10px;
  font: 650 0.85rem/1.4 var(--sans);
  color: var(--accent);
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
}
.cards button:hover { border-color: var(--accent); }


.foot {
  margin-top: 40px;
  padding-top: 18px;
  padding-bottom: 36px;
  font-size: 0.83rem;
  color: var(--muted);
}

@media (max-width: 520px) {
  .sheet { padding: 16px; }
  .alts li { gap: 6px; }
  .alts .label { flex-basis: 6.6em; font-size: 0.8rem; }
  .alts .val { font-size: 0.98rem; }
}

@media (max-width: 380px) {
  .device { padding: 10px; border-radius: 20px; }
  .keypad { gap: 6px; }
  .keypad button { height: 50px; }
  .keypad .unit { font-size: 0.62rem; }
  .keypad .unit b { font-size: 1.1rem; margin-left: 1px; }
  .result { font-size: 1.7rem; }
  .result.long { font-size: 1.3rem; }
  .fl { flex-basis: 6em; font-size: 0.66rem; }
}