:root {
  --bg: #111318;
  --panel: #1b1f27;
  --panel-2: #242936;
  --panel-3: #151923;
  --text: #f2f4f8;
  --muted: #aab2c0;
  --accent: #4f8cff;
  --accent-2: #6ee7b7;
  --accent-3: #f59e0b;
  --danger: #ef4444;
  --border: #343b4a;
  --code: #0c0f14;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  background: var(--bg);
  color: var(--text);
}

.app {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 280px 1fr;
}

.sidebar {
  background: #0e1117;
  border-right: 1px solid var(--border);
  padding: 22px;
  overflow-y: auto;
}

.brand {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 26px;
}

.logo {
  width: 52px;
  height: 52px;
  border-radius: 16px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #07111f;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
}

.brand h1 {
  font-size: 20px;
  margin: 0;
}

.brand p {
  color: var(--muted);
  margin: 3px 0 0;
  font-size: 13px;
}

.menu {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.menu button {
  text-align: left;
  background: transparent;
  color: var(--muted);
  border: 1px solid transparent;
  padding: 11px 12px;
  border-radius: 12px;
  cursor: pointer;
  font-size: 14px;
}

.menu button:hover {
  background: var(--panel);
  color: var(--text);
}

.menu button.active {
  background: var(--panel-2);
  color: var(--text);
  border-color: var(--accent);
}

.content {
  padding: 28px;
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.topbar {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  align-items: center;
}

.eyebrow {
  color: var(--accent-2);
  margin: 0 0 6px;
  font-size: 14px;
}

h2 {
  margin: 0;
  font-size: 32px;
}

.progress-wrap {
  width: 260px;
}

.progress-bar {
  height: 10px;
  background: var(--panel);
  border-radius: 99px;
  overflow: hidden;
  border: 1px solid var(--border);
}

#progressFill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  width: 10%;
  transition: width 0.25s ease;
}

.screen-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 24px;
  padding: 28px;
  min-height: 540px;
  box-shadow: 0 20px 70px rgba(0, 0, 0, 0.2);
}

.screen-card p,
.screen-card li {
  line-height: 1.6;
  color: #dce2ec;
  font-size: 18px;
}

.hero {
  display: grid;
  grid-template-columns: 1.12fr 0.88fr;
  gap: 26px;
  align-items: stretch;
}

.big-title {
  font-size: 46px;
  margin: 0 0 12px;
}

.lead {
  font-size: 21px;
  color: #e7ecf5;
  margin: 0 0 18px;
}

.highlight-box,
.visual-panel,
.activity-box,
.code-block,
.mini-card {
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: 20px;
}

.highlight-box {
  padding: 22px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.highlight-box h3,
.activity-box h3,
.visual-panel h3,
.mini-card h3 {
  margin: 0;
  color: var(--accent-2);
}

.highlight-box p,
.activity-box p {
  margin: 0;
}

.visual-panel {
  min-height: 230px;
  padding: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
}

.activity-box {
  margin-top: 22px;
  padding: 18px;
  border-left: 4px solid var(--accent-3);
}

.activity-box strong {
  color: #fde68a;
}

.pill-row,
.choice-row,
.file-row,
.rps-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.pill,
.file-pill {
  border: 1px solid var(--border);
  background: var(--panel-3);
  color: var(--text);
  border-radius: 99px;
  padding: 10px 13px;
  font-size: 15px;
}

.file-pill {
  color: #d1fae5;
  font-family: Consolas, monospace;
}

.code-block {
  background: var(--code);
  color: #d1fae5;
  padding: 18px;
  white-space: pre-wrap;
  overflow-x: auto;
  font-family: Consolas, monospace;
  font-size: 16px;
}

.mini-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(120px, 1fr));
  gap: 14px;
  margin-top: 18px;
}

.mini-card {
  padding: 16px;
}

.mini-card p {
  font-size: 16px;
  margin-bottom: 0;
}

.browser-mock {
  width: min(100%, 430px);
  background: #f8fafc;
  color: #111827;
  border-radius: 18px;
  overflow: hidden;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.25);
}

.browser-top {
  height: 38px;
  background: #dbe4f0;
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 0 12px;
}

.dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: #94a3b8;
}

.address {
  flex: 1;
  background: white;
  border-radius: 99px;
  padding: 5px 10px;
  color: #475569;
  font-size: 12px;
}

.browser-body {
  padding: 18px;
}

.mock-title {
  height: 20px;
  width: 70%;
  border-radius: 8px;
  background: #2563eb;
  margin-bottom: 14px;
}

.mock-line {
  height: 10px;
  border-radius: 99px;
  background: #cbd5e1;
  margin: 9px 0;
}

.mock-button {
  display: inline-block;
  background: #10b981;
  color: #052e20;
  border-radius: 10px;
  padding: 9px 12px;
  margin-top: 12px;
  font-weight: 700;
}

.server-visual {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 16px;
  width: 100%;
}

.server-box,
.client-box {
  background: #111827;
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 18px;
  text-align: center;
}

.server-stack {
  display: grid;
  gap: 8px;
}

.server-line {
  height: 28px;
  border-radius: 8px;
  background: linear-gradient(90deg, #4f8cff, #6ee7b7);
}

.arrow {
  color: var(--accent-2);
  font-size: 34px;
  font-weight: 800;
}

.folder-tree {
  width: min(100%, 430px);
}

.folder-title {
  color: #fde68a;
  font-weight: 700;
  margin-bottom: 12px;
}

.tree-row {
  background: #111827;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 12px;
  margin: 8px 0;
  font-family: Consolas, monospace;
  color: #d1fae5;
}

.split-visual {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  width: 100%;
}

.split-item {
  background: #111827;
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 16px;
  text-align: center;
}

.split-item strong {
  color: var(--accent-2);
  display: block;
  margin-bottom: 8px;
}

.flow-visual {
  width: 100%;
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 10px;
  align-items: center;
}

.flow-step {
  min-height: 86px;
  background: #111827;
  border: 1px solid var(--border);
  border-radius: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 12px;
  color: #e5e7eb;
  font-weight: 700;
}

.tech-visual {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
  width: 100%;
}

.tech-card {
  min-height: 150px;
  border-radius: 18px;
  padding: 18px;
  background: #111827;
  border: 1px solid var(--border);
}

.tech-card span {
  display: block;
  color: var(--accent-2);
  font-size: 34px;
  font-weight: 800;
  margin-bottom: 8px;
}

.rps-game {
  width: 100%;
  background: #111827;
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 18px;
}

.rps-row {
  margin: 12px 0;
}

.small-btn {
  border: 1px solid var(--border);
  background: #0c0f14;
  color: var(--text);
  border-radius: 12px;
  padding: 11px 14px;
  cursor: pointer;
  font-size: 15px;
}

.small-btn:hover {
  border-color: var(--accent);
}

.result-box {
  background: #0c0f14;
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px;
  min-height: 76px;
}

.navigation {
  display: flex;
  justify-content: space-between;
}

.btn {
  border: 0;
  padding: 13px 18px;
  border-radius: 14px;
  font-size: 16px;
  cursor: pointer;
}

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

.btn.secondary {
  background: var(--panel-2);
  color: var(--text);
  border: 1px solid var(--border);
}

.btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

@media (max-width: 1100px) {
  .hero,
  .server-visual,
  .split-visual,
  .tech-visual,
  .flow-visual,
  .mini-grid {
    grid-template-columns: 1fr;
  }

  .arrow {
    transform: rotate(90deg);
    text-align: center;
  }
}

@media (max-width: 900px) {
  .app {
    grid-template-columns: 1fr;
  }

  .sidebar {
    display: none;
  }

  .topbar {
    flex-direction: column;
    align-items: flex-start;
  }

  .progress-wrap {
    width: 100%;
  }

  .screen-card {
    padding: 20px;
  }

  .big-title {
    font-size: 34px;
  }
}