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

:root {
  --black: #000000;
  --near-black: #262626;
  --darkest: #090909;
  --white: #ffffff;
  --snow: #fafafa;
  --light-gray: #e5e5e5;
  --stone: #737373;
  --mid-gray: #525252;
  --silver: #a3a3a3;
  --btn-text: #404040;
  --border-light: #d4d4d4;
  --focus-ring: rgba(59, 130, 246, 0.5);
  --error: #dc2626;
  --error-border: #fca5a5;
  color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
  :root {
    --black: #ffffff;
    --near-black: #e5e5e5;
    --darkest: #fafafa;
    --white: #0a0a0a;
    --snow: #171717;
    --light-gray: #262626;
    --stone: #a3a3a3;
    --mid-gray: #d4d4d4;
    --silver: #737373;
    --btn-text: #d4d4d4;
    --border-light: #2e2e2e;
    --focus-ring: rgba(96, 165, 250, 0.4);
    --error: #f87171;
    --error-border: #7f1d1d;
  }

  select {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath d='M3 5l3 3 3-3' fill='none' stroke='%23a3a3a3' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  }

  .qr-area svg { filter: invert(1); }
}

body {
  font-family: ui-sans-serif, system-ui, -apple-system, system-ui, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
  background: var(--white);
  color: var(--black);
  min-height: 100vh;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

/* Navigation */
.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 24px;
  max-width: 1024px;
  margin: 0 auto;
}
.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--black);
}
.nav-brand svg { flex-shrink: 0; }
.nav-brand span {
  font-family: 'SF Pro Rounded', ui-sans-serif, system-ui, -apple-system, system-ui;
  font-size: 16px;
  font-weight: 500;
  color: var(--black);
}
.nav-steps {
  display: flex;
  gap: 6px;
  align-items: center;
}
.nav-step {
  width: 8px;
  height: 8px;
  border-radius: 9999px;
  background: var(--light-gray);
  transition: background 0.2s;
  cursor: pointer;
}
.nav-step.active { background: var(--black); }
.nav-step.done { background: var(--mid-gray); }

/* Container */
.container {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 24px 88px;
}

/* Hero / Page Title */
.page-hero {
  text-align: center;
  padding: 48px 0 40px;
}
.page-hero h1 {
  font-family: 'SF Pro Rounded', ui-sans-serif, system-ui, -apple-system, system-ui;
  font-size: 36px;
  font-weight: 500;
  line-height: 1.11;
  color: var(--black);
  margin-bottom: 12px;
}
.page-hero p {
  font-size: 18px;
  color: var(--stone);
  line-height: 1.56;
}

/* Steps */
.step { display: none; }
.step.active { display: block; }

/* Section heading */
.section-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 24px;
}
.section-head h2 {
  font-family: 'SF Pro Rounded', ui-sans-serif, system-ui, -apple-system, system-ui;
  font-size: 24px;
  font-weight: 500;
  line-height: 1.33;
  color: var(--black);
}
.section-head-actions {
  display: flex;
  gap: 16px;
  align-items: center;
}

/* Forms */
label {
  display: block;
  font-size: 14px;
  font-weight: 400;
  color: var(--mid-gray);
  margin-bottom: 6px;
}
select, input[type="text"], input[type="password"] {
  width: 100%;
  padding: 10px 16px;
  border: 1px solid var(--light-gray);
  border-radius: 9999px;
  font-size: 16px;
  font-family: inherit;
  color: var(--black);
  background: var(--white);
  outline: none;
  transition: border-color 0.15s;
  -webkit-appearance: none;
}
select {
  border-radius: 12px;
  cursor: pointer;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath d='M3 5l3 3 3-3' fill='none' stroke='%23737373' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  padding-right: 36px;
}
select:focus, input:focus {
  border-color: var(--black);
  box-shadow: 0 0 0 3px var(--focus-ring);
}
input::placeholder { color: var(--silver); }

.form-group { margin-bottom: 20px; }

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 24px;
  border: 1px solid transparent;
  border-radius: 9999px;
  font-size: 16px;
  font-family: inherit;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
  text-decoration: none;
  line-height: 1.5;
}
.btn-black {
  background: var(--black);
  color: var(--white);
  border-color: var(--black);
}
.btn-black:hover { background: var(--near-black); }
.btn-gray {
  background: var(--light-gray);
  color: var(--near-black);
  border-color: var(--light-gray);
}
.btn-gray:hover { background: var(--border-light); border-color: var(--border-light); }
.btn-white {
  background: var(--white);
  color: var(--btn-text);
  border-color: var(--border-light);
}
.btn-white:hover { background: var(--snow); }
.btn:disabled {
  background: var(--snow);
  color: var(--silver);
  border-color: var(--light-gray);
  cursor: not-allowed;
}
.btn-block { width: 100%; text-align: center; }

/* Link */
.link {
  color: var(--stone);
  cursor: pointer;
  font-size: 14px;
  text-decoration: none;
}
.link:hover { color: var(--black); }

/* Muted text */
.muted { color: var(--silver); font-size: 14px; }
.mt-12 { margin-top: 12px; }
.mt-16 { margin-top: 16px; }
.mt-24 { margin-top: 24px; }
.mb-8 { margin-bottom: 8px; }
.mb-16 { margin-bottom: 16px; }
.text-center { text-align: center; }
.flex-between { display: flex; justify-content: space-between; align-items: center; }

/* Toast */
.toast {
  display: none;
  padding: 12px 16px;
  border-radius: 12px;
  font-size: 14px;
  margin-bottom: 16px;
  line-height: 1.5;
  border: 1px solid;
}
.toast-error {
  background: var(--snow);
  color: var(--error);
  border-color: var(--error-border);
}

/* QR Area */
.qr-area {
  text-align: center;
  padding: 32px 0;
}
.qr-area svg { border-radius: 12px; background: var(--white); padding: 12px; }
.qr-area .hint {
  margin-top: 16px;
  font-size: 14px;
  color: var(--stone);
}

/* Category list */
.category-list {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin-bottom: 24px;
}
.category-item {
  padding: 12px 16px;
  border: 1px solid var(--light-gray);
  border-radius: 9999px;
  text-align: center;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
  font-size: 14px;
  color: var(--mid-gray);
}
.category-item:hover { border-color: var(--black); color: var(--black); }
.category-item.selected {
  background: var(--light-gray);
  border-color: var(--light-gray);
  color: var(--black);
  font-weight: 500;
}

/* Captcha */
.captcha-area {
  text-align: center;
  padding: 16px 0;
}
.captcha-area img {
  max-width: 280px;
  border-radius: 12px;
  border: 1px solid var(--light-gray);
  cursor: pointer;
}

/* Quiz area */
.quiz-area {
  max-height: 420px;
  overflow-y: auto;
}

/* Question cards */
.question-card {
  background: var(--snow);
  border-radius: 12px;
  padding: 16px 20px;
  margin-bottom: 8px;
  border: 1px solid var(--light-gray);
}
.question-card.correct { background: var(--white); border-color: var(--mid-gray); }
.question-card.wrong { background: var(--snow); border-color: var(--border-light); }

.question-num {
  font-size: 12px;
  color: var(--stone);
  font-weight: 500;
  margin-bottom: 4px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}
.question-text {
  font-size: 14px;
  color: var(--black);
  margin-bottom: 8px;
  line-height: 1.5;
}
.question-answer {
  font-size: 13px;
  color: var(--stone);
}
.question-answer .ai { color: var(--black); font-weight: 500; }
.question-answer .result { margin-left: 8px; }

/* Progress bar */
.progress-bar {
  height: 4px;
  background: var(--light-gray);
  border-radius: 9999px;
  margin-bottom: 24px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  background: var(--black);
  border-radius: 9999px;
  transition: width 0.3s;
}

/* Stats */
.stats {
  display: flex;
  justify-content: space-around;
  text-align: center;
  padding: 20px 0;
  border-top: 1px solid var(--light-gray);
  margin-bottom: 24px;
}
.stat-item .num {
  font-family: 'SF Pro Rounded', ui-sans-serif, system-ui, -apple-system, system-ui;
  font-size: 30px;
  font-weight: 500;
  color: var(--black);
  line-height: 1.2;
}
.stat-item .label { font-size: 12px; color: var(--stone); margin-top: 4px; }

/* Result card */
.result-card {
  text-align: center;
  padding: 40px 0 24px;
}
.result-card .score {
  font-family: 'SF Pro Rounded', ui-sans-serif, system-ui, -apple-system, system-ui;
  font-size: 56px;
  font-weight: 500;
  color: var(--black);
  line-height: 1;
}
.result-card .msg {
  font-size: 18px;
  color: var(--stone);
  margin-top: 12px;
}
.result-detail { margin-top: 24px; }
.result-detail h4 {
  font-size: 14px;
  font-weight: 500;
  color: var(--black);
  margin-bottom: 12px;
}
.result-detail .item {
  display: flex;
  justify-content: space-between;
  padding: 12px 0;
  border-bottom: 1px solid var(--light-gray);
  font-size: 14px;
  color: var(--mid-gray);
}
.result-detail .item:last-child { border-bottom: none; }

/* Log area */
.log-area {
  background: var(--snow);
  color: var(--stone);
  border-radius: 12px;
  border: 1px solid var(--light-gray);
  padding: 16px;
  font-family: ui-monospace, 'SFMono-Regular', Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', monospace;
  font-size: 12px;
  max-height: 160px;
  overflow-y: auto;
  margin-top: 16px;
  line-height: 1.63;
}
.log-area .log-info { color: var(--mid-gray); }
.log-area .log-success { color: var(--black); font-weight: 500; }
.log-area .log-error { color: var(--stone); }
.log-area .log-warn { color: var(--stone); }

/* Spinner */
.spinner {
  display: inline-block;
  width: 16px; height: 16px;
  border: 2px solid var(--light-gray);
  border-top: 2px solid var(--black);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  vertical-align: middle;
  margin-right: 6px;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* Logged in view */
.logged-status {
  font-size: 14px;
  color: var(--mid-gray);
  margin-bottom: 8px;
}
.logged-user { font-size: 12px; color: var(--silver); margin-bottom: 24px; }

/* Responsive */
@media (max-width: 640px) {
  .nav { padding: 12px 16px; }
  .container { padding: 0 16px 64px; }
  .page-hero { padding: 32px 0 28px; }
  .page-hero h1 { font-size: 30px; }
  .page-hero p { font-size: 16px; }
  .section-head h2 { font-size: 20px; }
  .category-list { grid-template-columns: 1fr; }
  .stats { gap: 8px; }
  .stat-item .num { font-size: 24px; }
  .result-card .score { font-size: 48px; }
  .btn { padding: 10px 20px; font-size: 14px; }
}

@media (max-width: 380px) {
  .nav-brand span { display: none; }
}