Layout and Demo Structure

This part handles the layout, cards, fake feed, alert overlay, and the question section at the bottom.

<div class="xss-concept-grid">
  <div class="xss-concept-card">...</div>
  <div class="xss-concept-card">...</div>
  <div class="xss-concept-card">...</div>
</div>

.xss-card {
  padding: 28px;
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
}

.xss-social-feed {
  padding: 16px;
  min-height: 110px;
}