/* ===== CSS Reset ===== */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* ===== Custom Properties ===== */
:root {
  --primary: #3B82F6;
  --primary-dark: #2563EB;
  --primary-light: #93C5FD;
  --primary-bg: #EFF6FF;
  --accent: #8B5CF6;
  --success: #22C55E;
  --error: #EF4444;
  --warning: #F59E0B;
  --bg: #F8FAFC;
  --surface: #FFFFFF;
  --surface-subtle: #F1F5F9;
  --surface-elevated: #FFFFFF;
  --text: #1E293B;
  --text-secondary: #64748B;
  --text-muted: #94A3B8;
  --border: #E2E8F0;
  --highlight-row: #EEF2F6;
  --highlight-num: #BAD7FD;
  --selected: #93C5FD;
  --cell-given: #0F172A;
  --cell-user: #1D4ED8;
  --board-border: #CBD5E1;
  --board-major-border: #0F172A;
  --cell-error-bg: #FEE2E2;
  --pause-bg: rgba(248, 250, 252, 0.95);
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.08);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.05);
}

/* ===== Dark Mode Theme Tokens ===== */
[data-theme="dark"] {
  --primary: #60A5FA;
  --primary-dark: #3B82F6;
  --primary-light: #93C5FD;
  --primary-bg: rgba(96, 165, 250, 0.16);
  --accent: #A78BFA;
  --success: #34D399;
  --error: #F87171;
  --warning: #FBBF24;
  --bg: #0F172A;
  --surface: #1E293B;
  --surface-subtle: #24334C;
  --surface-elevated: #283548;
  --text: #F1F5F9;
  --text-secondary: #94A3B8;
  --text-muted: #64748B;
  --border: #334155;
  --highlight-row: #24334C;
  --highlight-num: #1E3A8A;
  --selected: #2563EB;
  --cell-given: #F8FAFC;
  --cell-user: #60A5FA;
  --board-border: #334155;
  --board-major-border: #94A3B8;
  --cell-error-bg: rgba(239, 68, 68, 0.25);
  --pause-bg: rgba(15, 23, 42, 0.95);
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.45);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
}

/* ===== Tactile Action Buttons ===== */
.btn-tactile,
.btn-icon-tactile {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s ease;
  box-shadow: var(--shadow-sm);
  flex-shrink: 0;
}

.btn-tactile:hover,
.btn-icon-tactile:hover {
  background: var(--highlight-row);
  border-color: var(--primary-light);
  color: var(--primary);
  transform: translateY(-1px);
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.08);
}

.btn-tactile:active,
.btn-icon-tactile:active {
  transform: translateY(0) scale(0.94);
}

.btn-tactile svg,
.btn-icon-tactile svg {
  width: 16px;
  height: 16px;
}

/* ===== Smooth Theme Transitions ===== */
body,
.profile-card,
.modal,
.sudoku-board,
.cell,
.num-key,
.tool-btn,
.navbar,
.btn-pill,
.variant-card,
.chart-card,
.stat-card,
.btn-tactile,
.btn-icon-tactile,
.segmented-control,
.seg-btn {
  transition: background-color 0.22s ease, border-color 0.22s ease, color 0.22s ease, box-shadow 0.22s ease;
}

/* ===== Base Styles ===== */
html {
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
}

body {
  font-family: system-ui, -apple-system, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg);
  color: var(--text);
  min-height: 100vh;
  overflow: hidden;
  line-height: 1.5;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, svg {
  display: block;
  max-width: 100%;
}

svg {
  stroke-linecap: round;
  stroke-linejoin: round;
}

button {
  font-family: inherit;
  cursor: pointer;
}

input, textarea, select {
  font-family: inherit;
}

a {
  color: inherit;
  text-decoration: none;
}

ul, ol {
  list-style: none;
}

/* ===== Screen Transitions ===== */
.screen {
  position: fixed;
  inset: 0;
  display: flex;
  flex-direction: column;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity 0.3s ease, transform 0.3s ease, visibility 0.3s ease;
  transform: translateY(12px);
  z-index: 0;
}

.screen.active {
  opacity: 1;
  visibility: visible;
  pointer-events: all;
  transform: translateY(0);
  z-index: 10;
}

/* ===== Utility Classes ===== */
.hidden {
  display: none !important;
}

.text-center {
  text-align: center;
}

.text-secondary {
  color: var(--text-secondary);
}

/* ===== Gradient Text ===== */
.gradient-text {
  background: linear-gradient(135deg, var(--primary), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ===== Button Styles ===== */
.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  background-color: var(--primary);
  color: #FFFFFF;
  font-size: 0.95rem;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
  user-select: none;
}

.btn-primary:hover {
  background-color: var(--primary-dark);
  transform: translateY(-1px);
  box-shadow: 0 4px 16px rgba(59, 130, 246, 0.3);
}

.btn-primary:active {
  transform: scale(0.97);
  box-shadow: none;
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  background-color: transparent;
  color: var(--primary);
  font-size: 0.95rem;
  font-weight: 600;
  border: 1.5px solid var(--primary);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
  user-select: none;
}

.btn-secondary:hover {
  background-color: var(--primary-bg);
  transform: translateY(-1px);
}

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

.btn-text {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 20px;
  background: none;
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
  user-select: none;
}

.btn-text:hover {
  color: var(--text);
  background-color: var(--highlight-row);
}

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

.btn-danger {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  background-color: var(--error);
  color: #FFFFFF;
  font-size: 0.95rem;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
  user-select: none;
}

.btn-danger:hover {
  background-color: #DC2626;
  transform: translateY(-1px);
  box-shadow: 0 4px 16px rgba(239, 68, 68, 0.3);
}

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

.btn-large {
  width: 100%;
  height: 54px;
  font-size: 1.05rem;
  border-radius: var(--radius);
}

.btn-small {
  padding: 8px 16px;
  font-size: 0.85rem;
}

.btn-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 18px;
  border-radius: 50px;
  border: 1.5px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 0.85rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  user-select: none;
}

.btn-pill:hover {
  border-color: var(--primary-light);
  background: var(--primary-bg);
  color: var(--primary);
}

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

.btn-pill svg {
  width: 16px;
  height: 16px;
}

/* ===== Icon Buttons ===== */
.btn-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: transparent;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s ease;
  flex-shrink: 0;
}

.btn-icon:hover {
  background-color: var(--highlight-row);
  color: var(--text);
}

.btn-icon:active {
  transform: scale(0.92);
}

.btn-icon svg {
  width: 22px;
  height: 22px;
}

.btn-icon-sm {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: transparent;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s ease;
  flex-shrink: 0;
}

.btn-icon-sm:hover {
  background-color: var(--highlight-row);
  color: var(--text);
}

.btn-icon-sm:active {
  transform: scale(0.92);
}

.btn-icon-sm svg {
  width: 18px;
  height: 18px;
}

/* ===== Scrollbar Styling ===== */
::-webkit-scrollbar {
  width: 6px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-secondary);
}

/* ========================================
   MOBILE NOTICE OVERLAY (PC EXCLUSIVE DESIGN)
   ======================================== */
.mobile-notice-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.85);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 999999;
  align-items: center;
  justify-content: center;
  padding: 24px;
}

@media (max-width: 820px) {
  .mobile-notice-overlay:not(.dismissed) {
    display: flex;
  }
}

body.mobile-device .mobile-notice-overlay:not(.dismissed) {
  display: flex;
}

.mobile-notice-overlay.dismissed {
  display: none !important;
}

.mobile-notice-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg, 16px);
  padding: 32px 28px;
  max-width: 440px;
  width: 100%;
  text-align: center;
  box-shadow: 0 20px 45px rgba(0, 0, 0, 0.25);
  animation: modalPop 0.3s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex;
  flex-direction: column;
  align-items: center;
}

.mobile-notice-icon-wrapper {
  width: 84px;
  height: 84px;
  border-radius: 50%;
  background: var(--primary-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 16px;
  border: 2px solid var(--primary-light);
}

.mobile-notice-icon {
  width: 48px;
  height: 48px;
  color: var(--primary);
}

.mobile-notice-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  background: var(--primary-bg);
  color: var(--primary);
  border: 1px solid var(--primary-light);
  border-radius: 50px;
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 14px;
}

.mobile-notice-title {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 12px;
  line-height: 1.3;
}

.mobile-notice-desc {
  font-size: 0.92rem;
  color: var(--text);
  line-height: 1.55;
  margin-bottom: 10px;
}

.mobile-notice-note {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
  margin-bottom: 18px;
}

.mobile-notice-spec {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.78rem;
  color: var(--text-secondary);
  margin-bottom: 20px;
}

.mobile-notice-dismiss {
  color: var(--text-secondary);
  font-size: 0.85rem;
  text-decoration: underline;
  cursor: pointer;
  padding: 6px 12px;
}

.mobile-notice-dismiss:hover {
  color: var(--primary);
}