:root {
  /* ---- Default theme: BRAUN ET·26 ---- */
  --body-bg:             #000000;

  --display-bg:          #000000;
  --display-text:        #F4EFE0;
  --display-pip:         #A78BFA;
  --display-radius:      10px;
  --display-font:        "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;
  --result-size:         96px;
  --result-spacing:      -0.04em;
  --result-weight:       500;

  --secondary-text:      #B3AE9F;

  --key-digit-bg:        #E8E2D2;
  --key-digit-bg-press:  #D6D0C0;
  --key-digit-text:      #0E0E0E;
  --key-digit-shadow:    inset 0 -2px 0 rgba(0,0,0,0.06);

  --key-fn-bg:           #1F1F1F;
  --key-fn-bg-press:     #2A2A2A;
  --key-fn-text:         #F4EFE0;

  --key-op-bg:           #2A2A2A;
  --key-op-bg-press:     #363636;
  --key-op-text:         #F4EFE0;

  --key-eq-bg:           #8B5CF6;
  --key-eq-bg-press:     #A78BFA;
  --key-eq-text:         #FFFFFF;

  --tag-text:            #F4EFE0;
  --tag-size:            16px;
  --tag-spacing:         0.34em;
  --tag-weight:          600;

  --hint-text:           #6F6A60;
  --hairline:            rgba(255,255,255,0.05);

  --key-radius:          8px;
  --key-digit-size:      40px;
  --key-fn-size:         28px;
  --key-op-size:         46px;
  --key-eq-size:         52px;
  --key-font:            "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --key-weight:          500;
  --key-fn-weight:       600;

  --ui:   "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;
}

/* ============================================================
   THEME: CASIO F-91W (simplified)
   ============================================================ */
body[data-theme="casio"] {
  --body-bg:             #2E3133;

  --display-bg:          #A8B398;          /* LCD gray-green */
  --display-text:        #0F1308;
  --display-pip:         #C8423B;
  --display-radius:      4px;
  --display-font:        "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;
  --result-size:         78px;
  --result-spacing:      0.02em;
  --result-weight:       700;

  --secondary-text:      #444B36;

  --key-digit-bg:        #44484A;
  --key-digit-bg-press:  #54585A;
  --key-digit-text:      #E8E5DA;
  --key-digit-shadow:    inset 0 -2px 0 rgba(0,0,0,0.25), inset 0 1px 0 rgba(255,255,255,0.06);

  --key-fn-bg:           #5C6062;
  --key-fn-bg-press:     #6C7072;
  --key-fn-text:         #F0EDE2;

  --key-op-bg:           #44484A;
  --key-op-bg-press:     #54585A;
  --key-op-text:         #E8E5DA;

  --key-eq-bg:           #C8423B;
  --key-eq-bg-press:     #D8524B;
  --key-eq-text:         #FFFFFF;

  --tag-text:            #C8423B;
  --tag-spacing:         0.30em;
  --tag-weight:          700;

  --hint-text:           #6A6D62;
  --hairline:            rgba(0,0,0,0.25);

  --key-radius:          6px;
  --key-digit-size:      34px;
  --key-fn-size:         22px;
  --key-op-size:         34px;
  --key-eq-size:         34px;
}

body[data-theme="casio"] .display {
  box-shadow: inset 0 0 0 2px rgba(0,0,0,0.4), inset 0 0 18px rgba(0,0,0,0.15);
  background-image: repeating-linear-gradient(0deg, rgba(0,0,0,0.03) 0 1px, transparent 1px 3px);
}
body[data-theme="casio"] .tag {
  font-family: var(--ui);
}

/* ============================================================
   THEME: TI-83 PLUS (simplified)
   ============================================================ */
body[data-theme="ti83"] {
  --body-bg:             #2E3133;

  --display-bg:          #9CB37E;          /* faded LCD green */
  --display-text:        #0A1606;
  --display-pip:         #1E3A8A;
  --display-radius:      6px;
  --display-font:        "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;
  --result-size:         88px;
  --result-spacing:      -0.02em;
  --result-weight:       600;

  --secondary-text:      #2A3920;

  --key-digit-bg:        #15171A;
  --key-digit-bg-press:  #25272A;
  --key-digit-text:      #F2F2F2;
  --key-digit-shadow:    inset 0 -2px 0 rgba(0,0,0,0.5);

  --key-fn-bg:           #4A4D50;
  --key-fn-bg-press:     #5A5D60;
  --key-fn-text:         #FFFFFF;

  --key-op-bg:           #2D3033;
  --key-op-bg-press:     #3D4043;
  --key-op-text:         #FFFFFF;

  --key-eq-bg:           #1E3A8A;
  --key-eq-bg-press:     #2E4A9A;
  --key-eq-text:         #FFFFFF;

  --tag-text:            #DCDDDE;
  --tag-spacing:         0.22em;
  --tag-weight:          700;
  --tag-size:            17px;

  --hint-text:           #7A7D7F;
  --hairline:            rgba(255,255,255,0.06);

  --key-radius:          3px;
  --key-digit-size:      32px;
  --key-fn-size:         18px;
  --key-op-size:         34px;
  --key-eq-size:         28px;
}

body[data-theme="ti83"] .display {
  box-shadow: inset 0 0 0 3px #1A1D1F;
  background-image: repeating-linear-gradient(0deg, rgba(0,0,0,0.06) 0 1px, transparent 1px 3px);
}
body[data-theme="ti83"] .key {
  box-shadow: var(--key-digit-shadow), inset 0 0 0 1px rgba(255,255,255,0.04);
}
body[data-theme="ti83"] .key.op.primary {
  font-family: var(--ui);
  letter-spacing: 0.06em;
}

/* ============================================================
   BASE
   ============================================================ */
* { box-sizing: border-box; margin: 0; padding: 0; }

html, body {
  width: 600px;
  height: 600px;
  background: var(--body-bg);
  overflow: hidden;
  -webkit-user-select: none;
  user-select: none;
  transition: background 240ms ease;
}

body {
  font-family: var(--ui);
  -webkit-font-smoothing: antialiased;
  color: var(--tag-text);
}

.stage { width: 600px; height: 600px; position: relative; }

.screen {
  position: absolute;
  inset: 0;
  padding: 18px 22px 16px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

/* ---- Top bar ---- */
.bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 0 6px;
  height: 24px;
}

.tag {
  font-family: var(--ui);
  font-size: var(--tag-size);
  font-weight: var(--tag-weight);
  letter-spacing: var(--tag-spacing);
  text-transform: uppercase;
  color: #FFFFFF;
  background: transparent;
  border: 0;
  padding: 0;
  cursor: pointer;
  outline: none;
  transition: opacity 120ms ease, color 120ms ease;
}
.tag:hover  { opacity: 0.7; }
.tag:active { opacity: 0.5; }
.tag:focus,
.tag.is-focused {
  color: var(--key-eq-bg);
  opacity: 1;
  outline: none;
}

.tag.accent {
  font-family: var(--mono);
  font-size: 18px;
  font-weight: 500;
  letter-spacing: 0;
  color: var(--secondary-text);
  text-transform: none;
  cursor: default;
}

/* ---- Display ---- */
.display {
  background: var(--display-bg);
  border-radius: var(--display-radius);
  padding: 22px 28px 24px;
  min-height: 128px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  position: relative;
  box-shadow: inset 0 0 0 1px var(--hairline);
  transition: background 240ms ease;
}
.display::before {
  content: '';
  position: absolute;
  left: 20px;
  top: 22px;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--display-pip);
  box-shadow: 0 0 14px color-mix(in srgb, var(--display-pip) 50%, transparent);
}

.result {
  font-family: var(--display-font);
  font-size: var(--result-size);
  font-weight: var(--result-weight);
  line-height: 1.0;
  color: var(--display-text);
  font-variant-numeric: tabular-nums;
  letter-spacing: var(--result-spacing);
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  max-width: 100%;
  direction: ltr;
  text-align: right;
}
.result.error {
  color: var(--key-eq-bg);
  font-size: 64px;
  letter-spacing: 0.06em;
}

/* ---- Keypad ---- */
.pad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(5, 1fr);
  gap: 7px;
  flex: 1;
  min-height: 0;
}

.key {
  font-family: var(--key-font);
  font-size: var(--key-digit-size);
  font-weight: var(--key-weight);
  color: var(--key-digit-text);
  background: var(--key-digit-bg);
  border: 0;
  border-radius: var(--key-radius);
  cursor: pointer;
  outline: none;
  position: relative;
  transition: background 90ms cubic-bezier(0.2, 0, 0, 1),
              transform   80ms cubic-bezier(0.2, 0, 0, 1);
  font-variant-numeric: tabular-nums;
  box-shadow: var(--key-digit-shadow);
}

.key.fn {
  color: var(--key-fn-text);
  background: var(--key-fn-bg);
  font-size: var(--key-fn-size);
  font-weight: var(--key-fn-weight);
  letter-spacing: 0.02em;
  box-shadow: inset 0 0 0 1px var(--hairline);
}

.key.op {
  color: var(--key-op-text);
  background: var(--key-op-bg);
  font-size: var(--key-op-size);
  font-weight: var(--key-weight);
  box-shadow: inset 0 0 0 1px var(--hairline);
}

.key.wide {
  grid-column: span 2;
  text-align: left;
  padding-left: 64px;
}

.key:focus {
  outline: 3px solid var(--key-eq-bg);
  outline-offset: -3px;
}

.key.op.primary {
  background: var(--key-eq-bg);
  color: var(--key-eq-text);
  font-size: var(--key-eq-size);
  font-weight: 600;
  box-shadow: inset 0 -2px 0 rgba(0,0,0,0.18);
}
.key.op.primary:focus {
  outline-color: var(--tag-text);
}

.key.pressed                  { transform: scale(0.96); background: var(--key-digit-bg-press); }
.key.fn.pressed               { background: var(--key-fn-bg-press); }
.key.op.pressed               { background: var(--key-op-bg-press); }
.key.op.primary.pressed       { background: var(--key-eq-bg-press); }

/* ---- Hints ---- */
.hints {
  display: flex;
  justify-content: center;
  gap: 32px;
  padding-top: 4px;
}
.hint {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.24em;
  text-transform: uppercase;
  color: var(--hint-text);
}

@media (prefers-reduced-motion: reduce) {
  .key { transition: none; }
}