:root {
  --bg: #eef1f7;
  --bg-grad: radial-gradient(1200px 600px at 50% -10%, #ffffff 0%, #eef1f7 60%);
  --card: #ffffff;
  --text: #14181f;
  --muted: #5d6b7a;
  --accent: #2f6df6;
  --accent-contrast: #ffffff;
  --code-bg: #f3f5fa;
  --code-text: #14181f;
  --border: #e2e7f0;
  --switch-off: #c9d2e0;
  --shadow: 0 18px 50px rgba(20, 40, 80, 0.12);
}

html[data-theme="dark"] {
  --bg: #0e1117;
  --bg-grad: radial-gradient(1200px 600px at 50% -10%, #1a2230 0%, #0e1117 60%);
  --card: #161b24;
  --text: #e8edf4;
  --muted: #94a1b2;
  --accent: #4f8cff;
  --accent-contrast: #0e1117;
  --code-bg: #0b0f16;
  --code-text: #e8edf4;
  --border: #232b37;
  --switch-off: #2c3543;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.55);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  background: var(--bg-grad);
  background-color: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  transition: background-color .25s ease, color .25s ease;
}

.card {
  width: 100%;
  max-width: 460px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow);
  padding: 28px;
  transition: background-color .25s ease, border-color .25s ease;
}

.head h1 {
  margin: 0 0 6px;
  font-size: 1.35rem;
  letter-spacing: -0.02em;
}

.head .sub {
  margin: 0;
  color: var(--muted);
  font-size: .86rem;
  line-height: 1.5;
}

.head .sub code,
.formula code {
  background: var(--code-bg);
  padding: 1px 6px;
  border-radius: 6px;
  font-size: .85em;
}

/* ---- Display ---- */
.display {
  margin: 22px 0;
}

.code-label {
  font-size: .72rem;
  text-transform: uppercase;
  letter-spacing: .12em;
  color: var(--muted);
  margin-bottom: 8px;
}

.code {
  display: block;
  background: var(--code-bg);
  color: var(--code-text);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 16px;
  font-family: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 1.7rem;
  font-weight: 600;
  letter-spacing: .01em;
  word-break: break-all;
  line-height: 1.25;
}

.parts {
  margin-top: 14px;
  display: grid;
  gap: 8px;
}

.part {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  font-size: .85rem;
}

.part .k { color: var(--muted); }

.part .v {
  font-family: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  color: var(--text);
  text-align: right;
  word-break: break-all;
}

.part.formula .v { font-family: inherit; color: var(--muted); }

/* ---- Controls ---- */
.controls {
  display: grid;
  gap: 16px;
  padding-top: 20px;
  margin-top: 4px;
  border-top: 1px solid var(--border);
}

.control {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
}

.control-label {
  font-size: .92rem;
  font-weight: 500;
}

.hint {
  margin: -8px 0 0;
  font-size: .76rem;
  color: var(--muted);
  line-height: 1.45;
}

.text-input {
  flex: 0 0 auto;
  width: 150px;
  text-align: right;
  background: var(--code-bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 9px;
  padding: 9px 12px;
  font-family: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  font-size: .95rem;
  outline: none;
  transition: border-color .15s ease, box-shadow .15s ease;
}

.text-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 22%, transparent);
}

/* ---- Switch ---- */
.switch {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  cursor: pointer;
  user-select: none;
}

.switch-end {
  font-size: .78rem;
  color: var(--muted);
  font-family: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
}

.switch input {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
}

.track {
  position: relative;
  width: 46px;
  height: 26px;
  border-radius: 999px;
  background: var(--switch-off);
  transition: background-color .2s ease;
  flex: 0 0 auto;
}

.knob {
  position: absolute;
  top: 3px;
  left: 3px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #fff;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
  transition: transform .2s ease;
}

.switch input:checked + .track { background: var(--accent); }
.switch input:checked + .track .knob { transform: translateX(20px); }
.switch input:focus-visible + .track {
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 30%, transparent);
}

/* ---- Copy button ---- */
.copy {
  margin-top: 24px;
  width: 100%;
  border: none;
  border-radius: 11px;
  padding: 14px 16px;
  background: var(--accent);
  color: var(--accent-contrast);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform .08s ease, filter .15s ease;
}

.copy:hover { filter: brightness(1.05); }
.copy:active { transform: translateY(1px); }

.copy-msg {
  margin: 10px 0 0;
  min-height: 1.1em;
  text-align: center;
  font-size: .84rem;
  color: var(--accent);
  font-family: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  opacity: 0;
  transition: opacity .2s ease;
  word-break: break-all;
}

.copy-msg.show { opacity: 1; }

/* ---- Footer ---- */
.foot {
  margin-top: 22px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  text-align: center;
  font-size: .82rem;
  color: var(--muted);
}

.foot a { color: var(--muted); text-decoration: none; }
.foot a:hover { color: var(--accent); text-decoration: underline; }
.foot .dot { margin: 0 8px; }

/* ---- Legal page ---- */
.legal { max-width: 640px; text-align: left; }
.legal h1 { font-size: 1.4rem; margin: 0 0 4px; }
.legal h2 {
  font-size: .95rem;
  margin: 22px 0 6px;
  color: var(--accent);
}
.legal p { margin: 0; line-height: 1.6; font-size: .9rem; color: var(--text); }
.legal a { color: var(--accent); text-decoration: none; }
.legal a:hover { text-decoration: underline; }
.legal .back { display: inline-block; margin-bottom: 8px; font-size: .85rem; }