.app-header {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  padding: 0.75rem 1.5rem;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.logo {
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  white-space: nowrap;
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  color: var(--text-primary);
  text-decoration: none;
}
.logo:hover { text-decoration: none; color: var(--text-primary); }
.logo-icon { color: var(--accent); flex-shrink: 0; }
.logo-text { font-size: 1.05rem; }
.logo-accent { color: var(--accent); font-weight: 800; }

.header-nav { display: flex; gap: 0.25rem; margin-left: auto; position: relative; }
.header-link {
  font-size: 0.82rem;
  color: var(--text-secondary);
  padding: 0.3em 0.6em;
  border-radius: var(--radius);
  transition: color 0.1s, background 0.1s;
}
.header-link:hover { color: var(--text-primary); background: var(--bg-tertiary); text-decoration: none; }

.header-sep {
  color: var(--border); font-size: 0.8rem; margin: 0 0.1rem;
  user-select: none;
}

.icon-link {
  display: inline-flex; align-items: center;
  color: var(--text-secondary); padding: 0.3em 0.4em;
  border-radius: var(--radius); transition: color 0.1s, background 0.1s;
}
.icon-link:hover { color: var(--text-primary); background: var(--bg-tertiary); }

#app-main { max-width: 960px; margin: 0 auto; padding: 2rem 1.5rem; }
.loading { text-align: center; padding: 4rem 0; color: var(--text-muted); font-size: 1.1rem; }

.dashboard { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 1rem; }
.topic-hub { display: flex; flex-direction: column; gap: 0.75rem; }
.quiz-container { max-width: 700px; margin: 0 auto; }
.quiz-question { background: var(--bg-secondary); border: 1px solid var(--border); border-radius: var(--radius); padding: 2rem; margin-bottom: 1.5rem; }
.options-group { display: flex; flex-direction: column; gap: 0.6rem; margin: 1.2rem 0; }
.progress-bar { width: 100%; height: 4px; background: var(--bg-tertiary); border-radius: 2px; margin: 1rem 0; overflow: hidden; }
.progress-fill { height: 100%; background: var(--accent); border-radius: 2px; transition: width 0.3s ease; }

.summary-card { background: var(--bg-secondary); border: 1px solid var(--border); border-radius: var(--radius); padding: 2.5rem 2rem; text-align: center; max-width: 450px; margin: 2rem auto; }
.history-list { display: flex; flex-direction: column; gap: 0.5rem; }
.history-entry { display: flex; align-items: center; gap: 1rem; padding: 0.75rem 1rem; background: var(--bg-secondary); border: 1px solid var(--border); border-radius: var(--radius); }

.page-title { font-size: 1.3rem; font-weight: 600; margin-bottom: 1.5rem; }
.back-link {
  display: inline-flex; align-items: center; gap: 0.35rem;
  padding: 0.4em 0.8em; margin-bottom: 1.5rem; font-size: 0.8rem;
  background: var(--bg-secondary); color: var(--text-secondary);
  border: 1px solid var(--border); border-radius: var(--radius);
  text-decoration: none; transition: border-color 0.15s, color 0.15s;
}
.back-link:hover { border-color: var(--accent); color: var(--text-primary); text-decoration: none; }

@media (max-width: 600px) {
  #app-main { padding: 1rem; }
  .dashboard { grid-template-columns: 1fr; }
}