:root {
  --bg: #0f172a;
  --bg-soft: #111a32;
  --panel: #15213f;
  --text: #e6edf9;
  --text-soft: #9fb0d5;
  --accent: #2dd4bf;
  --accent-strong: #0ea5e9;
  --border: #243862;
  --shadow: rgba(0, 0, 0, 0.35);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  background:
    radial-gradient(circle at 15% 20%, #164e63 0%, transparent 35%),
    radial-gradient(circle at 85% 15%, #1d4ed8 0%, transparent 32%),
    linear-gradient(145deg, var(--bg) 0%, #030712 100%);
  font-family: "Trebuchet MS", "Segoe UI", Verdana, sans-serif;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border);
  background: rgba(17, 26, 50, 0.75);
  backdrop-filter: blur(6px);
  position: sticky;
  top: 0;
  z-index: 10;
}

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

.brand-mark {
  width: 2.25rem;
  height: 2.25rem;
  border-radius: 0.6rem;
  display: grid;
  place-items: center;
  font-weight: 700;
  color: #06242f;
  background: linear-gradient(135deg, var(--accent), #67e8f9);
  box-shadow: 0 8px 24px rgba(45, 212, 191, 0.35);
}

.brand h1 {
  margin: 0;
  font-size: 1.1rem;
}

.brand p {
  margin: 0.2rem 0 0;
  color: var(--text-soft);
  font-size: 0.82rem;
}

.tabs {
  display: flex;
  gap: 0.55rem;
  flex-wrap: wrap;
}

.tab {
  border: 1px solid var(--border);
  background: #111b36;
  color: var(--text);
  padding: 0.5rem 0.75rem;
  border-radius: 999px;
  cursor: pointer;
  transition: transform 180ms ease, background-color 180ms ease, border-color 180ms ease;
}

.tab:hover {
  transform: translateY(-1px);
  border-color: #3b82f6;
}

.tab.active {
  background: linear-gradient(135deg, #0ea5e9, #14b8a6);
  color: #03141c;
  border-color: transparent;
  font-weight: 700;
}

@media (max-width: 960px) {
  .topbar {
    flex-direction: column;
    align-items: stretch;
    gap: 0.75rem;
  }

  .tabs {
    width: 100%;
  }
}

.layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  padding: 1rem;
}

.panel {
  border: 1px solid var(--border);
  border-radius: 1rem;
  background: linear-gradient(165deg, rgba(21, 33, 63, 0.94), rgba(12, 20, 39, 0.92));
  box-shadow: 0 14px 30px var(--shadow);
}

.controls-panel {
  padding: 1rem;
}

.controls-grid {
  display: grid;
  gap: 0.85rem;
}

#comparison-mode-btn.is-on {
  background: linear-gradient(135deg, #22c55e, #10b981);
  color: #041b12;
  border-color: transparent;
  font-weight: 700;
}

.array-tools {
  display: grid;
  gap: 0.55rem;
  padding: 0.85rem;
  border: 1px solid rgba(59, 130, 246, 0.2);
  border-radius: 0.85rem;
  background: rgba(7, 12, 26, 0.35);
}

.array-tools label {
  font-weight: 600;
  color: var(--text-soft);
}

.array-input-row {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 0.6rem;
}

.array-input-row input {
  width: 100%;
  min-width: 0;
  border: 1px solid var(--border);
  border-radius: 0.7rem;
  padding: 0.65rem 0.8rem;
  color: var(--text);
  background: #0e1730;
  font: inherit;
}

.array-input-row input::placeholder {
  color: #7f90b8;
}

.array-input-row input:focus {
  outline: 2px solid rgba(103, 232, 249, 0.45);
  outline-offset: 1px;
}

.array-preset-row {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
}

.array-preset-row .btn {
  flex: 1 1 10rem;
}

.array-status {
  margin: 0;
  color: var(--text-soft);
  font-size: 0.88rem;
  line-height: 1.4;
  min-height: 1.25rem;
}

.array-status.is-error {
  color: #fca5a5;
}

.comparison-panel {
  padding: 1rem;
}

.comparison-head {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: flex-start;
}

.comparison-head h2,
.comparison-card h3 {
  margin: 0;
}

.comparison-head p,
.comparison-card p,
.comparison-status {
  margin: 0.35rem 0 0;
  color: var(--text-soft);
}

.comparison-actions {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
}

.comparison-config {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.75rem;
  margin-top: 1rem;
}

.comparison-config label {
  display: grid;
  gap: 0.45rem;
  color: var(--text-soft);
  font-weight: 600;
}

.comparison-config select {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 0.7rem;
  padding: 0.65rem 0.8rem;
  color: var(--text);
  background: #0e1730;
  font: inherit;
}

.comparison-config select:focus {
  outline: 2px solid rgba(103, 232, 249, 0.45);
  outline-offset: 1px;
}

.comparison-status {
  grid-column: 1 / -1;
  min-height: 1.4rem;
}

.comparison-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.comparison-card {
  border: 1px solid rgba(59, 130, 246, 0.18);
  border-radius: 1rem;
  background: rgba(8, 13, 28, 0.56);
  padding: 0.9rem;
}

.comparison-card-head {
  display: flex;
  justify-content: space-between;
  gap: 0.75rem;
  align-items: baseline;
}

.comparison-time {
  color: #93c5fd;
  font-weight: 700;
  white-space: nowrap;
}

.comparison-stats {
  display: flex;
  gap: 0.9rem;
  flex-wrap: wrap;
  margin-top: 0.45rem;
  color: var(--text-soft);
  font-weight: 600;
}

.comparison-bars {
  margin-top: 0.75rem;
  height: 320px;
  min-height: 320px;
}

.btn {
  border: 1px solid var(--border);
  background: #162547;
  color: var(--text);
  border-radius: 0.7rem;
  padding: 0.6rem 0.9rem;
  cursor: pointer;
  transition:
    background-color 160ms ease,
    transform 160ms ease,
    border-color 160ms ease,
    box-shadow 160ms ease,
    filter 160ms ease;
}

.btn:hover:not(:disabled) {
  background: #203361;
  transform: translateY(-1px);
}

.btn:active:not(:disabled),
.btn.flash-click:not(:disabled) {
  transform: translateY(1px) scale(0.98);
  filter: brightness(1.08);
}

.btn:focus-visible {
  outline: 2px solid #93c5fd;
  outline-offset: 2px;
}

.btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.btn-primary {
  background: linear-gradient(135deg, #0ea5e9, #14b8a6);
  color: #062231;
  border: none;
  font-weight: 700;
}

.btn.is-on {
  border-color: #67e8f9;
  box-shadow: 0 0 0 1px rgba(103, 232, 249, 0.35), 0 10px 22px rgba(14, 165, 233, 0.35);
}

#play-btn.is-on {
  background: linear-gradient(135deg, #22c55e, #34d399);
  color: #04210f;
}

#pause-btn.is-on {
  background: linear-gradient(135deg, #f59e0b, #fbbf24);
  color: #261702;
  border-color: transparent;
}

#reset-btn.flash-click:not(:disabled) {
  background: linear-gradient(135deg, #f97316, #ef4444);
  color: #290404;
  border-color: transparent;
}

.btn-secondary {
  background: #1f2f59;
  font-weight: 600;
}

.button-row {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
}

.speed-control {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 0.6rem;
  align-items: center;
}

.speed-control input {
  width: 100%;
}

.stats {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  color: var(--text-soft);
  font-weight: 600;
}

.explanation-panel {
  padding: 1rem;
}

.explanation-panel h2 {
  margin: 0 0 0.5rem;
  font-size: 1rem;
}

.explanation-panel p {
  margin: 0;
  line-height: 1.45;
  color: var(--text-soft);
  min-height: 5rem;
}

.guide-panel {
  padding: 1rem;
}

.performance-panel,
.quiz-panel {
  padding: 1rem;
}

.panel-head h2 {
  margin: 0;
  font-size: 1.05rem;
}

.panel-head p {
  margin: 0.35rem 0 0;
  color: var(--text-soft);
}

.chart-wrap {
  margin-top: 0.9rem;
  padding: 0.85rem;
  border: 1px solid rgba(59, 130, 246, 0.18);
  border-radius: 0.95rem;
  background: rgba(8, 13, 28, 0.5);
}

.chart-wrap canvas {
  width: 100% !important;
  display: block;
}

.quiz-form {
  display: grid;
  gap: 0.85rem;
  margin-top: 0.9rem;
}

.quiz-card {
  border: 1px solid rgba(59, 130, 246, 0.18);
  border-radius: 0.9rem;
  background: rgba(8, 13, 28, 0.5);
  padding: 0.85rem;
}

.quiz-card h3 {
  margin: 0 0 0.55rem;
  font-size: 0.96rem;
}

.quiz-options {
  display: grid;
  gap: 0.45rem;
}

.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 0.55rem;
  color: #dbe7ff;
}

.quiz-option input {
  margin-top: 0.2rem;
}

.quiz-actions {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-top: 0.9rem;
}

.quiz-score {
  color: #93c5fd;
  font-weight: 700;
}

.quiz-feedback {
  margin: 0.65rem 0 0;
  color: var(--text-soft);
  min-height: 1.3rem;
}

.quiz-feedback.is-error {
  color: #fca5a5;
}

.guide-head h2 {
  margin: 0;
  font-size: 1.05rem;
}

.guide-head p {
  margin: 0.35rem 0 0;
  color: var(--text-soft);
  font-size: 0.9rem;
}

.guide-grid {
  margin-top: 0.9rem;
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.85rem;
}

.guide-card {
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  background: rgba(8, 13, 28, 0.5);
  padding: 0.85rem;
}

.guide-card h3 {
  margin: 0 0 0.45rem;
  font-size: 0.95rem;
}

.guide-card p {
  margin: 0;
  line-height: 1.5;
  color: #dbe7ff;
}

.guide-complexity {
  margin-top: 0.65rem !important;
  color: #93c5fd !important;
  font-weight: 600;
}

.guide-code {
  margin: 0;
  border-radius: 0.7rem;
  border: 1px solid rgba(59, 130, 246, 0.35);
  background: #050a1a;
  color: #dbeafe;
  padding: 0.75rem;
  line-height: 1.45;
  font-size: 0.82rem;
  overflow: auto;
  white-space: pre;
}

@media (min-width: 1024px) {
  .layout {
    grid-template-columns: 3fr 1.15fr;
    grid-template-areas:
      "controls controls"
      "performance performance"
      "visualizer explanation"
      "guide guide";
    align-items: start;
  }

  .controls-panel {
    grid-area: controls;
  }

  .visualizer-panel {
    grid-area: visualizer;
  }

  .performance-panel {
    grid-area: performance;
  }

  .explanation-panel {
    grid-area: explanation;
    position: sticky;
    top: 5.7rem;
  }

  .guide-panel {
    grid-area: guide;
  }

  .guide-grid {
    grid-template-columns: 1.15fr 1fr;
  }

  .comparison-head,
  .comparison-card-head {
    align-items: center;
  }
}

@media (max-width: 700px) {
  .topbar {
    padding: 0.9rem;
  }

  .brand {
    width: 100%;
  }

  .brand h1 {
    font-size: 1rem;
  }

  .tabs {
    width: 100%;
  }

  .tab {
    min-width: 0;
    flex: 1 1 calc(50% - 0.55rem);
    text-align: center;
  }

  .speed-control {
    grid-template-columns: 1fr;
  }

  .array-input-row {
    grid-template-columns: 1fr;
  }

  .comparison-head,
  .comparison-config,
  .comparison-grid {
    grid-template-columns: 1fr;
  }

  .comparison-head {
    display: grid;
  }

  .comparison-card-head {
    display: grid;
    align-items: start;
  }

  .comparison-bars {
    height: 260px;
    min-height: 260px;
  }

  .quiz-actions {
    align-items: stretch;
  }
}

@media (max-width: 430px) {
  .tabs {
    gap: 0.45rem;
  }

  .tab {
    flex: 1 1 100%;
  }
}