@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600&family=JetBrains+Mono:wght@400;600&display=swap');

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

*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg-page:       #f0f2f7;
  --bg-card:       #ffffff;
  --bg-header:     #1a1f36;
  --text-primary:  #1a1f36;
  --text-secondary: #6b7280;
  --text-muted:    #9ca3af;
  --border:        #e5e7eb;
  --border-hover:  #d1d5db;
  --accent:        #4f6ef7;
  --accent-dark:   #3451d1;
  --accept-bg:     #ecfdf5;
  --accept-border: #10b981;
  --accept-text:   #065f46;
  --reject-bg:     #fef2f2;
  --reject-border: #ef4444;
  --reject-text:   #991b1b;
  --cell-head-bg:  #eff2fe;
  --cell-head-bd:  #4f6ef7;
  --cell-head-tx:  #3451d1;
  --cell-x-bg:     #fff7ed;
  --cell-x-bd:     #f97316;
  --cell-x-tx:     #9a3412;
  --cell-y-bg:     #ecfdf5;
  --cell-y-bd:     #10b981;
  --cell-y-tx:     #065f46;
  --shadow:        0 1px 3px rgba(0, 0, 0, 0.08),
                   0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md:     0 4px 6px rgba(0, 0, 0, 0.07),
                   0 2px 4px rgba(0, 0, 0, 0.05);
}

[data-theme="dark"] {
  --bg-page:       #0f1117;
  --bg-card:       #1a1d27;
  --bg-header:     #0f1117;
  --text-primary:  #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted:    #64748b;
  --border:        #2d3148;
  --border-hover:  #3d4268;
  --accent:        #6b8aff;
  --accent-dark:   #4f6ef7;
  --accept-bg:     #052e16;
  --accept-border: #10b981;
  --accept-text:   #6ee7b7;
  --reject-bg:     #2d0f0f;
  --reject-border: #ef4444;
  --reject-text:   #fca5a5;
  --cell-head-bg:  #1e2456;
  --cell-head-bd:  #6b8aff;
  --cell-head-tx:  #a5b4fc;
  --cell-x-bg:     #2d1a06;
  --cell-x-bd:     #f97316;
  --cell-x-tx:     #fdba74;
  --cell-y-bg:     #052e16;
  --cell-y-bd:     #10b981;
  --cell-y-tx:     #6ee7b7;
  --shadow:        0 1px 3px rgba(0, 0, 0, 0.4);
  --shadow-md:     0 4px 6px rgba(0, 0, 0, 0.3);
}

body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg-page);
  color: var(--text-primary);
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

/* HEADER */
header {
  background: var(--bg-header);
  color: white;
  padding: 2rem 1rem 1.8rem;
  text-align: center;
  position: relative;
}
header h1 {
  font-size: 1.9rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  color: white;
}

header .subtitle {
  margin-top: 0.4rem;
  font-size: 1rem;
  opacity: 0.6;
  font-family: 'JetBrains Mono', monospace;
}

/* THEME TOGGLE */
.theme-toggle {
  position: absolute;
  top: 1.2rem;
  right: 1.5rem;
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: 20px;
  padding: 6px 14px;
  color: white;
  cursor: pointer;
  font-size: 13px;
  font-family: 'Inter', sans-serif;
  display: flex;
  align-items: center;
  gap: 6px;
  transition: background 0.2s;
}

.theme-toggle:hover {
  background: rgba(255, 255, 255, 0.18);
}

/* MAIN */
main {
  max-width: 880px;
  margin: 2rem auto;
  padding: 0 1rem;
  display: flex;
  flex-direction: column;
  gap: 1.1rem;
}

/* CARDS */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.2rem 1.4rem;
  box-shadow: var(--shadow);
  transition: background 0.3s, border 0.3s;
}

/* EXAMPLES */
.examples {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}
.label {
  font-size: 13px;
  color: var(--text-secondary);
  font-weight: 500;
}
.ex-btn {
  padding: 5px 14px;
  border-radius: 20px;
  border: 1.5px solid;
  background: transparent;
  cursor: pointer;
  font-size: 13px;
  font-weight: 500;
  font-family: 'JetBrains Mono', monospace;
  transition: background 0.15s;
}

.ex-btn.valid {
  border-color: var(--accept-border);
  color: var(--accept-text);
}

.ex-btn.valid:hover {
  background: var(--accept-bg);
}

.ex-btn.invalid {
  border-color: var(--reject-border);
  color: var(--reject-text);
}

.ex-btn.invalid:hover {
  background: var(--reject-bg);
}

.ex-btn.active {
  background: var(--cell-head-bg);
  border-color: var(--accent);
  color: var(--accent);
}

/* INPUT ROW */
.input-row {
  display: flex;
  gap: 8px;
}
.input-row input {
  flex: 1;
  padding: 9px 14px;
  border-radius: 10px;
  border: 1.5px solid var(--border);
  font-size: 15px;
  font-family: 'JetBrains Mono', monospace;
  background: var(--bg-card);
  color: var(--text-primary);
  outline: none;
  transition: border 0.2s, background 0.3s;
}

.input-row input:focus {
  border-color: var(--accent);
}

.input-row input::placeholder {
  color: var(--text-muted);
}

/* BUTTONS */
.btn {
  padding: 9px 20px;
  border-radius: 10px;
  border: 1.5px solid var(--border);
  background: var(--bg-card);
  color: var(--text-primary);
  cursor: pointer;
  font-size: 14px;
  font-family: 'Inter', sans-serif;
  font-weight: 500;
  transition: background 0.15s, border 0.15s, transform 0.1s;
}

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

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

.btn.primary {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

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

.btn:disabled {
  opacity: 0.35;
  cursor: not-allowed;
  transform: none;
}

/* TAPE */
.tape-section {
  overflow-x: auto;
  padding: 1.4rem 1rem;
}
.arrow-row, .tape-row {
  display: flex;
  justify-content: center;
  gap: 5px;
  min-width: max-content;
  margin: 0 auto;
}
.arrow-row { margin-bottom: 4px; }

.cell, .arrow-cell {
  width: 46px;
  height: 46px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 19px;
  font-weight: 600;
  font-family: 'JetBrains Mono', monospace;
  flex-shrink: 0;
}
.cell {
  border: 1.5px solid var(--border);
  border-radius: 8px;
  background: var(--bg-card);
  color: var(--text-primary);
  transition: background 0.2s, border-color 0.2s, color 0.2s;
}

.cell.head {
  border: 2.5px solid var(--cell-head-bd);
  background: var(--cell-head-bg);
  color: var(--cell-head-tx);
}

.cell.marked-x {
  background: var(--cell-x-bg);
  border-color: var(--cell-x-bd);
  color: var(--cell-x-tx);
}

.cell.marked-y {
  background: var(--cell-y-bg);
  border-color: var(--cell-y-bd);
  color: var(--cell-y-tx);
}

.cell.end-cell {
  background: var(--bg-page);
  color: var(--text-muted);
  border-color: var(--border);
}

.arrow-cell {
  color: var(--accent);
  font-size: 16px;
}

/* INFO ROW */
.info-row {
  display: flex;
  gap: 1rem;
}
.info-card {
  flex: 1;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1rem 1.4rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  box-shadow: var(--shadow);
}
.info-label { font-size: 12px; color: var(--text-muted); font-weight: 500; text-transform: uppercase; letter-spacing: 0.05em; }
.state-pill {
  font-size: 20px;
  font-weight: 600;
  color: var(--accent);
  font-family: 'JetBrains Mono', monospace;
}

.state-pill.accept {
  color: var(--accept-border);
}

.state-pill.reject {
  color: var(--reject-border);
}
.step-num { font-size: 20px; font-weight: 600; font-family: 'JetBrains Mono', monospace; }

/* MSG BOX */
.msg-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: 10px;
  padding: 12px 16px;
  font-size: 13.5px;
  color: var(--text-secondary);
  font-family: 'JetBrains Mono', monospace;
  min-height: 48px;
  transition: background 0.3s, border 0.3s;
  box-shadow: var(--shadow);
}

.msg-box.accept {
  border-left-color: var(--accept-border);
  background: var(--accept-bg);
  color: var(--accept-text);
}

.msg-box.reject {
  border-left-color: var(--reject-border);
  background: var(--reject-bg);
  color: var(--reject-text);
}

/* BTN ROW */
.btn-row { display: flex; gap: 8px; flex-wrap: wrap; }

/* SPEED */
.speed-row {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 13px;
  color: var(--text-secondary);
}
.speed-row input[type=range] { width: 100px; accent-color: var(--accent); }

/* LEGEND */
.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 13px;
  color: var(--text-secondary);
}
.leg-item {
  display: flex;
  align-items: center;
  gap: 7px;
}

.leg-box {
  width: 18px;
  height: 18px;
  border-radius: 5px;
  border: 1.5px solid;
  display: inline-block;
}

.head-color {
  background: var(--cell-head-bg);
  border-color: var(--cell-head-bd);
}

.x-color {
  background: var(--cell-x-bg);
  border-color: var(--cell-x-bd);
}

.y-color {
  background: var(--cell-y-bg);
  border-color: var(--cell-y-bd);
}

.end-color {
  background: var(--bg-page);
  border-color: var(--border);
}

/* FOOTER */
footer {
  text-align: center;
  padding: 2rem 1rem;
  font-size: 13px;
  color: var(--text-muted);
}
footer a {
  color: var(--accent);
  text-decoration: none;
}

footer a:hover {
  text-decoration: underline;
}