:root {
  --primary-blue: #2196f3;
  --primary-blue-dark: #1976d2;
  --primary-green: #43a047;
  --primary-green-dark: #2e7d32;

  --bg-gradient: linear-gradient(135deg, #e0f7fa 0%, #e8eaf6 100%);
  --text-main: #334155;
  --text-secondary: #64748b;
  --card-bg: rgba(255, 255, 255, 0.65);
  --card-border: rgba(255, 255, 255, 0.8);

  --font-main: "Noto Sans TC", "Microsoft JhengHei", Arial, sans-serif;
}

body {
  background: var(--bg-gradient);
  background-attachment: fixed;
  color: var(--text-main);
  font-family: var(--font-main);
  margin: 0;
  padding: 0;
}

header,
main {
  width: 100%;
  max-width: 800px;
  margin: 0 auto;
}

header {
  padding: 2em 0 1em 0;
  text-align: center;
}

main {
  padding: 1em 0 2em 0;
}

section {
  background: var(--card-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid var(--card-border);
  border-radius: 20px;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
  padding: 2em;
  margin-bottom: 2em;
}

h1,
h2 {
  color: var(--text-main);
}

ul {
  margin-left: 1.5em;
}

a {
  color: var(--primary-blue);
  text-decoration: underline;
}

.btn-row {
  display: flex;
  gap: 1em;
  justify-content: center;
  margin-top: 2em;
}

.invite-btn {
  display: inline-block;
  padding: 16px 32px;
  border-radius: 50px;
  font-weight: bold;
  text-decoration: none;
  color: #fff;
  transition: transform 0.2s, box-shadow 0.2s, background 0.2s;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.invite-btn:hover {
  transform: translateY(-2px);
}

.invite-btn.blue {
  background: var(--primary-blue);
  box-shadow: 0 4px 15px rgba(33, 150, 243, 0.4);
}

.invite-btn.blue:hover {
  background: var(--primary-blue-dark);
  box-shadow: 0 6px 20px rgba(33, 150, 243, 0.6);
}

.invite-btn.green {
  background: var(--primary-green);
  box-shadow: 0 4px 15px rgba(67, 160, 71, 0.4);
}

.invite-btn.green:hover {
  background: var(--primary-green-dark);
  box-shadow: 0 6px 20px rgba(67, 160, 71, 0.6);
}

.site-footer {
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 2em 0 1em 0;
  background: transparent;
  padding: 1em 0;
  font-size: 1em;
  color: var(--text-secondary);
}