:root {
  --body-top: #1d2430;
  --body-bottom: #0c1017;
  --shell-top: #4b5567;
  --shell-bottom: #252d39;
  --shell-edge: #141922;
  --screen: #dce7b3;
  --screen-top: #e8f0c3;
  --screen-text: #1c2910;
  --screen-dim: #60714a;
  --key-text: #f4f7fb;
  --key-fn-top: #677287;
  --key-fn-bottom: #424b5d;
  --key-num-top: #5d6470;
  --key-num-bottom: #383f49;
  --key-op-top: #4f6b95;
  --key-op-bottom: #304661;
  --key-danger-top: #7a5050;
  --key-danger-bottom: #553636;
  --key-enter-top: #7d9079;
  --key-enter-bottom: #4d614b;
  --border: #11151c;
  --shadow: rgba(0, 0, 0, 0.35);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: Arial, sans-serif;
  background:
    radial-gradient(circle at top, rgba(255, 255, 255, 0.08), transparent 30%),
    linear-gradient(180deg, var(--body-top), var(--body-bottom));
  color: #f3f6fb;
}

.wrap {
  max-width: 760px;
  margin: 0 auto;
  padding: 28px 18px 40px;
}

.calc {
  background: linear-gradient(180deg, var(--shell-top), var(--shell-bottom));
  border: 1px solid var(--shell-edge);
  border-radius: 28px;
  padding: 18px;
  box-shadow:
    0 24px 60px var(--shadow),
    inset 0 1px 0 rgba(255, 255, 255, 0.12),
    inset 0 -2px 0 rgba(0, 0, 0, 0.28);
}

.brand {
  color: #f7f8fc;
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin-bottom: 14px;
  gap: 12px;
}

.brand h1 {
  margin: 0;
  font-size: 20px;
  letter-spacing: 0.08em;
}

.brand small {
  color: #cfd6e2;
}

.screen {
  background: linear-gradient(180deg, var(--screen-top), var(--screen));
  color: var(--screen-text);
  border: 3px solid #829366;
  border-radius: 14px;
  padding: 14px 16px;
  min-height: 196px;
  font-family: "Courier New", monospace;
  display: grid;
  grid-template-rows: auto auto 1fr;
  gap: 10px;
  box-shadow:
    inset 0 2px 8px rgba(60, 80, 28, 0.18),
    0 8px 16px rgba(0, 0, 0, 0.18);
}

.screen-top {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  font-size: 12px;
  color: var(--screen-dim);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.stack {
  border-top: 1px solid rgba(28, 41, 16, 0.24);
  padding-top: 10px;
  line-height: 1.5;
  font-size: 18px;
  white-space: pre-wrap;
}

.stack-line {
  display: grid;
  grid-template-columns: 26px 1fr;
  gap: 8px;
  padding: 2px 4px;
  border-radius: 4px;
}

.stack-line.selected {
  background: rgba(28, 41, 16, 0.12);
  outline: 1px dashed rgba(28, 41, 16, 0.4);
}

.stack-line.moving {
  background: rgba(117, 160, 90, 0.2);
  outline: 1px solid rgba(28, 41, 16, 0.5);
}

.stack-line .label {
  text-align: right;
  color: var(--screen-dim);
}

.stack-line.selected .label,
.stack-line.moving .label {
  color: var(--screen-text);
  font-weight: bold;
}

#display {
  font-size: 18px;
  font-weight: bold;
  letter-spacing: 0.04em;
}

.hidden-input {
  position: absolute;
  left: -9999px;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.topbar {
  margin-top: 14px;
  display: grid;
  grid-template-columns: minmax(120px, 148px) minmax(132px, 160px) 1fr minmax(72px, 88px) minmax(108px, 128px) minmax(72px, 88px);
  gap: 10px;
  align-items: stretch;
}

.topbar-cell,
.topbar-status {
  min-height: 70px;
  background: rgba(6, 10, 16, 0.18);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: 16px;
  padding: 10px;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.05);
}

.menu-cell {
  position: relative;
}

.topbar-label {
  display: block;
  margin-bottom: 6px;
  font-size: 11px;
  color: #d9e1ec;
  text-transform: uppercase;
  letter-spacing: 0.12em;
}

.status {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  color: #edf2fa;
  font-size: 12px;
  align-content: center;
}

.pill {
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 999px;
  padding: 6px 10px;
  background: rgba(255, 255, 255, 0.06);
}

.menu-trigger {
  width: 100%;
  min-height: 38px;
}

.popup-menu {
  position: absolute;
  top: calc(100% + 8px);
  left: 10px;
  right: 10px;
  z-index: 20;
  display: grid;
  gap: 8px;
  padding: 10px;
  border-radius: 14px;
  background: rgba(18, 24, 34, 0.96);
  border: 1px solid rgba(255, 255, 255, 0.08);
  box-shadow: 0 16px 30px rgba(0, 0, 0, 0.35);
}

.popup-menu[hidden] {
  display: none;
}

.popup-menu-compact {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.hidden-select {
  position: absolute;
  left: -9999px;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.action-cell {
  display: flex;
  align-items: stretch;
}

.action-cell > button {
  width: 100%;
}

.topbar-status {
  display: flex;
  align-items: center;
}

select,
button {
  border-radius: 12px;
  border: 1px solid var(--border);
  font: inherit;
}

select {
  padding: 10px 12px;
  background: #edf1f7;
  color: #111;
}

.keyboard-layout {
  margin-top: 18px;
  display: grid;
  grid-template-columns: 4fr 3fr 2fr;
  gap: 12px;
}

.key-group {
  background: rgba(6, 10, 16, 0.18);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: 18px;
  padding: 12px;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.05);
}

.group-title {
  margin: 0 0 10px;
  color: #dce4f0;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.14em;
}

.key-grid {
  display: grid;
  gap: 10px;
}

.functions-grid {
  grid-template-columns: repeat(4, minmax(0, 1fr));
  grid-template-rows: repeat(4, 56px);
}

.numbers-grid {
  grid-template-columns: repeat(3, minmax(0, 1fr));
  grid-template-rows: repeat(4, 56px);
}

.operators-grid {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  grid-template-rows: repeat(4, 56px);
}

.key-spacer {
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.03);
  border: 1px dashed rgba(255, 255, 255, 0.04);
}

button {
  padding: 10px 8px;
  color: var(--key-text);
  cursor: pointer;
  font-weight: bold;
  box-shadow:
    inset 0 1px 0 rgba(255, 255, 255, 0.12),
    0 3px 0 rgba(0, 0, 0, 0.25);
  transition: filter 120ms ease, transform 120ms ease;
}

button:hover { filter: brightness(1.08); }
button:active {
  transform: translateY(2px);
  box-shadow:
    inset 0 1px 0 rgba(255, 255, 255, 0.08),
    0 1px 0 rgba(0, 0, 0, 0.25);
}

.key-function {
  background: linear-gradient(180deg, var(--key-fn-top), var(--key-fn-bottom));
}

.key-number {
  background: linear-gradient(180deg, var(--key-num-top), var(--key-num-bottom));
}

.key-operator {
  background: linear-gradient(180deg, var(--key-op-top), var(--key-op-bottom));
}

.key-danger {
  background: linear-gradient(180deg, var(--key-danger-top), var(--key-danger-bottom));
}

.key-enter {
  background: linear-gradient(180deg, var(--key-enter-top), var(--key-enter-bottom));
  grid-row: span 2;
}

.error {
  margin-top: 12px;
  min-height: 20px;
  color: #ff9f9f;
  font-family: "Courier New", monospace;
  font-size: 13px;
}

.hint {
  color: #cfd7e3;
  margin-top: 10px;
  font-size: 12px;
  line-height: 1.5;
}

@media (max-width: 980px) {
  .topbar {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
}

@media (max-width: 860px) {
  .keyboard-layout {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 640px) {
  .wrap {
    padding: 14px;
  }

  .calc {
    padding: 14px;
    border-radius: 22px;
  }

  .brand {
    flex-direction: column;
    align-items: flex-start;
  }

  .topbar {
    grid-template-columns: 1fr;
  }

  .functions-grid,
  .numbers-grid,
  .operators-grid {
    grid-template-rows: repeat(4, 52px);
  }
}