/* ==========================================================================
   SUDOKU NEXUS - CORE DESIGN SYSTEM & GLASSMORPHISM STYLES
   ========================================================================== */

:root {
  /* Color Palette - Cyber / Neon Dark Theme */
  --bg-dark: #070913;
  --bg-card: rgba(18, 24, 43, 0.7);
  --bg-card-border: rgba(255, 255, 255, 0.08);
  --bg-hover: rgba(255, 255, 255, 0.06);

  /* Primary Accent Gradients */
  --accent-cyan: #00f2fe;
  --accent-blue: #4facfe;
  --accent-purple: #7f00ff;
  --accent-magenta: #e100ff;
  --gradient-primary: linear-gradient(135deg, var(--accent-cyan), var(--accent-blue));
  --gradient-accent: linear-gradient(135deg, var(--accent-purple), var(--accent-magenta));
  --gradient-glow: linear-gradient(135deg, rgba(0,242,254,0.3), rgba(127,0,255,0.3));

  /* Game Colors */
  --cell-bg: rgba(15, 22, 40, 0.85);
  --cell-given-fg: #f0f4f8;
  --cell-user-fg: #38ef7d;
  --cell-candidate-fg: rgba(255, 255, 255, 0.45);
  
  /* State Highlights */
  --hl-selected: rgba(0, 242, 254, 0.25);
  --hl-selected-border: #00f2fe;
  --hl-peer: rgba(79, 172, 254, 0.1);
  --hl-same-num: rgba(225, 0, 255, 0.22);
  --hl-error: rgba(255, 75, 75, 0.25);
  --hl-error-fg: #ff4b4b;
  --hl-trying: rgba(255, 187, 0, 0.35);
  --hl-backtrack: rgba(255, 50, 100, 0.35);
  --hl-hint: rgba(0, 255, 170, 0.35);

  /* Text Colors */
  --text-main: #f1f5f9;
  --text-muted: #94a3b8;
  --text-dim: #64748b;

  /* Typography */
  --font-sans: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;

  /* Shadows & Effects */
  --shadow-lg: 0 20px 40px -15px rgba(0, 0, 0, 0.6);
  --shadow-glow: 0 0 25px rgba(0, 242, 254, 0.25);
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
}

/* Global Reset & Base Styles */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-dark);
  color: var(--text-main);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow-x: hidden;
  position: relative;
}

/* Background Ambient Glow Orbs */
.app-background {
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  overflow: hidden;
}

.bg-glow {
  position: absolute;
  border-radius: 50%;
  filter: blur(100px);
  opacity: 0.35;
  animation: floatOrb 20s infinite alternate ease-in-out;
}

.bg-glow-1 {
  width: 500px;
  height: 500px;
  background: var(--accent-cyan);
  top: -150px;
  left: -150px;
}

.bg-glow-2 {
  width: 600px;
  height: 600px;
  background: var(--accent-purple);
  bottom: -200px;
  right: -150px;
  animation-delay: -7s;
}

.bg-glow-3 {
  width: 400px;
  height: 400px;
  background: var(--accent-magenta);
  top: 40%;
  left: 50%;
  transform: translate(-50%, -50%);
  animation-delay: -14s;
}

@keyframes floatOrb {
  0% { transform: translate(0, 0) scale(1); }
  50% { transform: translate(60px, 40px) scale(1.1); }
  100% { transform: translate(-40px, 80px) scale(0.95); }
}

/* Main Container Shell */
.app-container {
  position: relative;
  z-index: 1;
  width: 100%;
  max-width: 1200px;
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

/* Header Styles */
.app-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.5rem 0.25rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.85rem;
}

.brand-icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-md);
  background: var(--gradient-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #050a14;
  box-shadow: var(--shadow-glow);
}

.brand h1 {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.1;
}

.gradient-text {
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.subtitle {
  font-size: 0.825rem;
  color: var(--text-muted);
  font-weight: 400;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.timer-badge {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 0.9rem;
  border-radius: var(--radius-sm);
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--bg-card-border);
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--accent-cyan);
}

/* Glassmorphic Cards */
.glass-card {
  background: var(--bg-card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--bg-card-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  box-shadow: var(--shadow-lg);
}

/* Control Bar & Segmented Selector */
.difficulty-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
  padding: 0.85rem 1.25rem;
}

.difficulty-selector {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.difficulty-selector .label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
}

.segmented-control {
  display: flex;
  background: rgba(0, 0, 0, 0.4);
  padding: 4px;
  border-radius: var(--radius-md);
  border: 1px solid var(--bg-card-border);
}

.segment-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.45rem 0.9rem;
  font-family: var(--font-sans);
  font-size: 0.825rem;
  font-weight: 600;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s ease;
}

.segment-btn:hover {
  color: var(--text-main);
}

.segment-btn.active {
  background: var(--gradient-primary);
  color: #040914;
  box-shadow: 0 4px 12px rgba(0, 242, 254, 0.3);
}

.action-group {
  display: flex;
  gap: 0.75rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.6rem 1.1rem;
  font-family: var(--font-sans);
  font-size: 0.875rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

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

.btn-primary {
  background: var(--gradient-primary);
  color: #040914;
  box-shadow: 0 4px 14px rgba(0, 242, 254, 0.25);
}

.btn-primary:hover {
  box-shadow: 0 6px 20px rgba(0, 242, 254, 0.4);
  transform: translateY(-1px);
}

.btn-secondary {
  background: rgba(255, 255, 255, 0.06);
  color: var(--text-main);
  border: 1px solid var(--bg-card-border);
}

.btn-secondary:hover {
  background: rgba(255, 255, 255, 0.12);
  border-color: rgba(255, 255, 255, 0.2);
}

.btn-danger {
  background: rgba(255, 75, 75, 0.15);
  color: #ff4b4b;
  border: 1px solid rgba(255, 75, 75, 0.3);
}

.btn-danger:hover {
  background: rgba(255, 75, 75, 0.25);
}

.btn-icon-only {
  padding: 0.6rem;
  border-radius: var(--radius-sm);
}

.btn-full {
  width: 100%;
}

.btn-sm {
  padding: 0.35rem 0.75rem;
  font-size: 0.775rem;
  border-radius: var(--radius-sm);
}

/* Main Layout Grid */
.main-layout {
  display: grid;
  grid-template-columns: minmax(320px, 540px) 1fr;
  gap: 1.5rem;
  align-items: start;
}

/* Status Banner */
.status-banner {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background: rgba(18, 24, 43, 0.6);
  border: 1px solid var(--bg-card-border);
  padding: 0.65rem 1rem;
  border-radius: var(--radius-md);
  margin-bottom: 0.85rem;
  font-size: 0.875rem;
}

.status-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--accent-cyan);
  box-shadow: 0 0 10px var(--accent-cyan);
  animation: pulseDot 2s infinite;
}

.status-banner.solving .status-dot {
  background: #ffbb00;
  box-shadow: 0 0 10px #ffbb00;
}

.status-banner.solved .status-dot {
  background: #38ef7d;
  box-shadow: 0 0 10px #38ef7d;
}

.status-banner.error .status-dot {
  background: #ff4b4b;
  box-shadow: 0 0 10px #ff4b4b;
}

@keyframes pulseDot {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.5; transform: scale(0.85); }
}

/* 9x9 Sudoku Grid */
.sudoku-grid-wrapper {
  position: relative;
  width: 100%;
  aspect-ratio: 1 / 1;
  background: rgba(10, 14, 26, 0.95);
  border-radius: var(--radius-lg);
  padding: 8px;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.8), 0 0 30px rgba(0, 242, 254, 0.08);
  border: 2px solid rgba(255, 255, 255, 0.1);
}

.sudoku-grid {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(9, 1fr);
  width: 100%;
  height: 100%;
  border-radius: 12px;
  overflow: hidden;
  gap: 1px;
  background: rgba(255, 255, 255, 0.08);
}

/* Individual Cell Styling */
.cell {
  position: relative;
  background: var(--cell-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: clamp(1.2rem, 3.5vw, 1.8rem);
  font-weight: 700;
  cursor: pointer;
  user-select: none;
  transition: background-color 0.15s ease, border-color 0.15s ease, transform 0.1s ease;
}

/* 3x3 Block Thicker Dividers */
.cell[data-col="2"], .cell[data-col="5"] {
  border-right: 3px solid rgba(0, 242, 254, 0.4);
}

.cell[data-row="2"], .cell[data-row="5"] {
  border-bottom: 3px solid rgba(0, 242, 254, 0.4);
}

/* Cell States & Cell Values */
.cell.given {
  color: var(--cell-given-fg);
  font-weight: 800;
}

.cell.user-input {
  color: var(--accent-cyan);
  text-shadow: 0 0 10px rgba(0, 242, 254, 0.4);
}

.cell.peer-highlight {
  background: var(--hl-peer);
}

.cell.same-num-highlight {
  background: var(--hl-same-num);
}

.cell.selected {
  background: var(--hl-selected) !important;
  box-shadow: inset 0 0 0 2px var(--hl-selected-border);
  z-index: 2;
}

.cell.error {
  background: var(--hl-error) !important;
  color: var(--hl-error-fg) !important;
  animation: shake 0.3s ease;
}

/* Solver Visual Animation States */
.cell.state-trying {
  background: var(--hl-trying) !important;
  color: #ffdd67 !important;
  transform: scale(1.05);
  z-index: 3;
}

.cell.state-backtrack {
  background: var(--hl-backtrack) !important;
  color: #ff6b8b !important;
}

.cell.state-hint {
  background: var(--hl-hint) !important;
  color: #00ffaa !important;
  animation: pulseHint 1.2s infinite;
}

@keyframes pulseHint {
  0%, 100% { box-shadow: inset 0 0 0 2px #00ffaa; }
  50% { box-shadow: inset 0 0 0 4px #00ffaa; }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-4px); }
  75% { transform: translateX(4px); }
}

/* Pencil Mark Candidate 3x3 Sub-Grid */
.candidate-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  padding: 2px;
  pointer-events: none;
}

.candidate-num {
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: clamp(0.55rem, 1.3vw, 0.75rem);
  font-weight: 600;
  color: var(--cell-candidate-fg);
}

/* Gameplay Toolbar */
.game-toolbar {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 0.5rem;
  margin-top: 0.85rem;
}

.tool-btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.25rem;
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--bg-card-border);
  color: var(--text-muted);
  padding: 0.6rem 0.25rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  font-family: var(--font-sans);
  font-size: 0.725rem;
  font-weight: 600;
  position: relative;
  transition: all 0.2s ease;
}

.tool-btn:hover {
  background: rgba(255, 255, 255, 0.1);
  color: var(--text-main);
}

.tool-btn.active {
  background: rgba(0, 242, 254, 0.15);
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
}

.accent-tool {
  background: var(--gradient-accent);
  color: #fff;
  border: none;
}

.accent-tool:hover {
  box-shadow: 0 4px 15px rgba(225, 0, 255, 0.4);
  transform: translateY(-1px);
}

.badge {
  position: absolute;
  top: -4px;
  right: -4px;
  background: #334155;
  color: #fff;
  font-size: 0.6rem;
  padding: 1px 4px;
  border-radius: 4px;
}

.tool-btn.active .badge {
  background: var(--accent-cyan);
  color: #000;
}

/* Sidebar Column */
.sidebar-column {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

/* Card Header */
.card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

.card-header h3, .card-header h4 {
  font-size: 1.05rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--text-main);
}

.status-pill {
  font-size: 0.725rem;
  font-weight: 700;
  padding: 0.25rem 0.65rem;
  border-radius: 20px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.status-pill.idle {
  background: rgba(255, 255, 255, 0.08);
  color: var(--text-muted);
}

.status-pill.running {
  background: rgba(0, 242, 254, 0.2);
  color: var(--accent-cyan);
  box-shadow: 0 0 10px rgba(0, 242, 254, 0.3);
}

.status-pill.paused {
  background: rgba(255, 187, 0, 0.2);
  color: #ffbb00;
}

.solver-actions-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
  margin-bottom: 1rem;
}

.btn-visual-solve {
  background: var(--gradient-primary);
  color: #040914;
}

.btn-instant-solve {
  background: var(--gradient-accent);
  color: #fff;
}

.solver-control-group {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

/* Speed Slider Container */
.speed-slider-container {
  background: rgba(0, 0, 0, 0.3);
  padding: 0.85rem 1rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--bg-card-border);
  margin-bottom: 1rem;
}

.speed-label-row {
  display: flex;
  justify-content: space-between;
  font-size: 0.825rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
}

.mono-highlight {
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--accent-cyan);
}

.custom-range {
  width: 100%;
  accent-color: var(--accent-cyan);
  cursor: pointer;
}

.speed-ticks {
  display: flex;
  justify-content: space-between;
  font-size: 0.675rem;
  color: var(--text-dim);
  margin-top: 0.25rem;
}

/* Metrics Grid */
.metrics-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem;
}

.metric-box {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--bg-card-border);
  padding: 0.6rem 0.4rem;
  border-radius: var(--radius-sm);
  text-align: center;
}

.metric-value {
  display: block;
  font-size: 1rem;
}

.metric-label {
  font-size: 0.675rem;
  color: var(--text-dim);
  text-transform: uppercase;
}

/* Virtual Numpad */
.numpad-card {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.numpad-grid {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  gap: 0.4rem;
}

.numpad-btn {
  aspect-ratio: 1 / 1;
  background: rgba(255, 255, 255, 0.06);
  border: 1px solid var(--bg-card-border);
  border-radius: var(--radius-md);
  color: var(--text-main);
  font-family: var(--font-mono);
  font-size: 1.15rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s ease;
}

.numpad-btn:hover {
  background: var(--gradient-primary);
  color: #040914;
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 242, 254, 0.3);
}

.numpad-bottom-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem;
}

/* Hint Card */
.hint-card {
  border-color: rgba(0, 255, 170, 0.3);
  background: rgba(10, 30, 25, 0.85);
}

.hint-content {
  font-size: 0.875rem;
  line-height: 1.5;
  color: var(--text-main);
}

.btn-close-sm {
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 1.25rem;
  cursor: pointer;
}

/* Modal Windows */
.modal-overlay {
  position: fixed;
  inset: 0;
  z-index: 100;
  background: rgba(5, 8, 16, 0.85);
  backdrop-filter: blur(12px);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  opacity: 1;
  transition: opacity 0.25s ease;
}

.modal-overlay.hidden {
  display: none;
  opacity: 0;
  pointer-events: none;
}

.modal-box {
  width: 100%;
  max-width: 520px;
  border-color: rgba(255, 255, 255, 0.15);
}

.modal-lg {
  max-width: 680px;
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

.modal-header h3 {
  font-size: 1.25rem;
  font-weight: 700;
}

.modal-close {
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 1.5rem;
  cursor: pointer;
}

.modal-close:hover {
  color: #fff;
}

.modal-desc {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.input-group label {
  display: block;
  font-size: 0.825rem;
  color: var(--text-muted);
  margin-bottom: 0.35rem;
}

textarea#importBoardString {
  width: 100%;
  background: rgba(0, 0, 0, 0.4);
  border: 1px solid var(--bg-card-border);
  border-radius: var(--radius-sm);
  color: var(--accent-cyan);
  font-family: var(--font-mono);
  font-size: 0.875rem;
  padding: 0.65rem;
  resize: vertical;
}

.preset-samples {
  margin-top: 1rem;
}

.preset-samples .label {
  display: block;
  font-size: 0.825rem;
  color: var(--text-dim);
  margin-bottom: 0.5rem;
}

.sample-buttons {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.modal-footer {
  display: flex;
  justify-content: flex-end;
  gap: 0.75rem;
  margin-top: 1.25rem;
}

/* Algorithm Guide Styling */
.algorithm-guide {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.guide-section h4 {
  font-size: 0.975rem;
  color: var(--accent-cyan);
  margin-bottom: 0.35rem;
}

.guide-section p {
  font-size: 0.875rem;
  line-height: 1.55;
  color: var(--text-muted);
}

.legend-items {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.825rem;
  color: var(--text-main);
}

.legend-box {
  width: 18px;
  height: 18px;
  border-radius: 4px;
}

.utility-hidden {
  display: none !important;
}

.mt-2 { margin-top: 0.75rem; }
.hidden { display: none !important; }

/* Responsive Media Queries */
@media (max-width: 900px) {
  .main-layout {
    grid-template-columns: 1fr;
  }
  
  .numpad-grid {
    gap: 0.25rem;
  }
  
  .numpad-btn {
    font-size: 1rem;
  }
}

@media (max-width: 600px) {
  .app-container {
    padding: 0.75rem;
  }
  
  .app-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.75rem;
  }
  
  .header-actions {
    width: 100%;
    justify-content: space-between;
  }
  
  .difficulty-bar {
    flex-direction: column;
    align-items: stretch;
  }
  
  .segmented-control {
    overflow-x: auto;
  }

  .game-toolbar {
    grid-template-columns: repeat(3, 1fr);
  }
}