* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #f4f6f8;
  color: #1f2937;
}
.container {
  width: min(100% - 28px, 900px);
  margin: 30px auto 50px;
}
.card {
  background: white;
  border-radius: 16px;
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: 0 5px 20px rgba(0,0,0,.07);
}
h1, h2 { margin-top: 0; }
.subtitle, .muted { color: #6b7280; }
label {
  display: block;
  margin: 16px 0 7px;
  font-weight: 600;
}
input, select {
  width: 100%;
  padding: 13px 14px;
  border: 1px solid #d1d5db;
  border-radius: 10px;
  font-size: 16px;
  background: white;
}
button {
  border: 0;
  border-radius: 10px;
  padding: 13px 18px;
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  background: #2563eb;
  color: white;
}
button:disabled {
  opacity: .55;
  cursor: not-allowed;
}
form button {
  width: 100%;
  margin-top: 20px;
}
.secondary {
  background: #e5e7eb;
  color: #111827;
}
.section-header {
  display: flex;
  justify-content: space-between;
  gap: 15px;
  align-items: center;
}
.topics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 14px;
}
.topic {
  border: 1px solid #e5e7eb;
  border-radius: 12px;
  padding: 16px;
}
.topic.full {
  background: #fafafa;
}
.topic-title {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  font-weight: 700;
}
.badge {
  white-space: nowrap;
  font-size: 13px;
  padding: 4px 8px;
  border-radius: 999px;
  background: #e5e7eb;
}
.participants {
  margin: 12px 0 0;
  padding-left: 20px;
}
.message {
  margin-top: 16px;
  padding: 12px 14px;
  border-radius: 10px;
}
.message.success { background: #dcfce7; color: #166534; }
.message.error { background: #fee2e2; color: #991b1b; }
.message.info { background: #dbeafe; color: #1e40af; }

@media (max-width: 600px) {
  .container { margin-top: 14px; }
  .card { padding: 18px; border-radius: 12px; }
  .section-header { align-items: flex-start; flex-direction: column; }
  .secondary { width: 100%; }
}