:root {
  --color-bg: #0f172a;
  --color-card: #14213d;
  --color-screen: #0a1326;
  --color-screen-text: #e2e8f0;
  --color-accent: #fcd34d;
  --color-accent-strong: #f59e0b;
  --color-end: #ef4444;
  --color-key-bg: #1e293b;
  --color-key-bg-hover: #334155;
  --color-text: #f8fafc;
  --color-text-soft: #cbd5e1;
  --color-text-muted: #94a3b8;
  --radius-md: 14px;
  --radius-lg: 22px;
  --shadow-soft: 0 12px 32px rgba(8, 12, 24, 0.55);
  --font-mono: "SFMono-Regular", Menlo, Consolas, monospace;
  --font-sans: "Inter", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-sans);
  -webkit-font-smoothing: antialiased;
}

.masthead {
  padding: 1.5rem 1.5rem 0.5rem;
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.masthead h1 {
  margin: 0;
  font-size: 1.7rem;
}

.subtitle {
  margin: 0;
  color: var(--color-text-soft);
}

.subtitle code {
  background: rgba(252, 211, 77, 0.18);
  color: var(--color-accent);
  padding: 0.05rem 0.4rem;
  border-radius: 6px;
  font-family: var(--font-mono);
}

.masthead nav {
  margin-top: 0.6rem;
  display: flex;
  gap: 0.75rem;
}

.masthead a {
  color: var(--color-accent);
  text-decoration: none;
  font-size: 0.9rem;
}

.masthead a:hover {
  text-decoration: underline;
}

.stage {
  max-width: 1200px;
  margin: 1rem auto 4rem;
  padding: 0 1.5rem;
  display: grid;
  grid-template-columns: minmax(260px, 380px) 1fr;
  gap: 2rem;
  align-items: start;
}

.phone {
  background: var(--color-card);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  box-shadow: var(--shadow-soft);
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.screen {
  background: var(--color-screen);
  border-radius: var(--radius-md);
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
  font-family: var(--font-mono);
  color: var(--color-screen-text);
  min-height: 220px;
}

.screen-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8rem;
  color: var(--color-text-muted);
}

.dot {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 999px;
  background: #475569;
}

.dot-idle {
  background: #475569;
}
.dot-active {
  background: #4ade80;
  box-shadow: 0 0 12px rgba(74, 222, 128, 0.6);
}
.dot-end {
  background: var(--color-end);
}
.dot-error {
  background: #f87171;
}

.screen-body {
  margin: 0;
  flex: 1;
  white-space: pre-wrap;
  word-wrap: break-word;
  font-size: 0.95rem;
  line-height: 1.4;
}

.display {
  width: 100%;
  background: rgba(255, 255, 255, 0.05);
  color: var(--color-screen-text);
  border: 1px solid rgba(248, 250, 252, 0.1);
  border-radius: 10px;
  padding: 0.65rem 0.8rem;
  font-family: var(--font-mono);
  font-size: 1rem;
  letter-spacing: 0.06em;
}

.display:focus {
  outline: none;
  border-color: var(--color-accent);
}

.keypad {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.6rem;
}

.key {
  background: var(--color-key-bg);
  color: var(--color-text);
  border: none;
  border-radius: 14px;
  padding: 1rem 0.5rem;
  font-size: 1.4rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  transition: background 0.12s ease, transform 0.05s ease;
}

.key small {
  font-size: 0.65rem;
  color: var(--color-text-muted);
  font-weight: 400;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.key:hover {
  background: var(--color-key-bg-hover);
}

.key:active {
  transform: scale(0.97);
}

.actions {
  display: grid;
  grid-template-columns: 1.5fr 1fr 1fr;
  gap: 0.5rem;
}

.btn {
  background: var(--color-key-bg);
  color: var(--color-text);
  border: none;
  border-radius: 12px;
  padding: 0.85rem 0.5rem;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
}

.btn:hover {
  background: var(--color-key-bg-hover);
}

.btn-primary {
  background: var(--color-accent);
  color: #1f2937;
}

.btn-primary:hover {
  background: var(--color-accent-strong);
}

.btn-end {
  background: var(--color-end);
}

.btn-end:hover {
  background: #dc2626;
}

.trace {
  background: var(--color-card);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  box-shadow: var(--shadow-soft);
  max-height: 80vh;
  overflow-y: auto;
}

.trace h2 {
  margin-top: 0;
  font-size: 1.1rem;
}

#trace {
  list-style: decimal inside;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

#trace li {
  background: rgba(255, 255, 255, 0.04);
  border-radius: 10px;
  padding: 0.6rem 0.75rem;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-text-soft);
  white-space: pre-wrap;
  word-wrap: break-word;
}

#trace li.input {
  color: var(--color-accent);
}

#trace li.error {
  color: #f87171;
}

.trace details {
  margin-top: 1.5rem;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

.trace details summary {
  cursor: pointer;
  color: var(--color-accent);
}

@media (max-width: 820px) {
  .stage {
    grid-template-columns: 1fr;
  }
  .phone {
    max-width: 380px;
    margin: 0 auto;
  }
}