:root {
  --bg-gradient: linear-gradient(180deg, #eef5f2, #d9f3e4, #bde2cc);
  --text-color: #1a3b2e;
  --accent: #2e7d32;
  --muted: #4e6f55;
  --link-color: #225d37;
  --header-bg: rgba(220, 255, 240, 0.95);
}
html, body {
  margin: 0;
  height: 100%;
  font-family: "Poppins", sans-serif;
  background: var(--bg-gradient);
  color: var(--text-color);
  transition: background 0.9s ease, color 0.6s ease;
}

.mode-input {
  position: absolute;
  left: -9999px;
}

header {
  background: var(--header-bg);
  padding: 18px 12px;
  text-align: center;
  position: sticky;
  top: 0;
  z-index: 1200;
  box-shadow: 0 2px 10px rgba(0,0,0,0.18);
}

header h1 {
  margin: 0;
  color: var(--accent);
  font-size: 1.9rem;
  font-weight: 700;
}

.nav-links {
  display: flex;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.nav-links a {
  color: var(--link-color);
  text-decoration: none;
  padding: 6px 10px;
  border-radius: 8px;
  font-weight: 600;
  font-size: 0.98rem;
  transition: background .25s ease, color .25s ease, transform .18s ease;
}

.nav-links a:hover,
.nav-links a.active {
  background: rgba(255,255,255,0.18);
  color: #fff;
  transform: translateY(-2px);
}

.mode-switch {
  position: fixed;
  top: 78px;
  right: 20px;
  display: flex;
  gap: 10px;
  z-index: 2100;
}

.mode-switch label {
  cursor: pointer;
  font-size: 1.2rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 6px;
  border-radius: 8px;
  transition: transform .25s ease, text-shadow .25s ease;
  background: rgba(255,255,255,0.02);
}

.mode-switch label:hover {
  transform: scale(1.08);
}

main {
  padding: 30px 18px 60px;
  text-align: center;
  background: var(--bg-gradient);
  color: var(--text-color);
  transition: background 0.9s ease, color 0.6s ease;
}

h2 { color: var(--accent); margin-top: 6px; }
h3 { color: var(--accent); margin-top: 18px; }

p {
  max-width: 900px;
  margin: 10px auto;
  line-height: 1.65;
  font-size: 1rem;
  padding: 0 12px;
}

.research-img {
  width: 280px;
  max-width: 80%;
  height: auto;
  display: block;
  margin: 25px auto;
  border-radius: 10px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.25);
  transition: transform 0.3s ease, box-shadow 0.3s ease;
  object-fit: cover;
}

.research-img:hover {
  transform: scale(1.05);
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.4);
}

.research-list {
  list-style: none;
  padding: 0;
  max-width: 760px;
  margin: 18px auto;
}

.research-list li {
  background: rgba(255,255,255,0.06);
  margin: 8px 0;
  padding: 12px;
  border-radius: 8px;
  transition: transform .25s ease, background .25s ease;
}

.research-list li:hover {
  transform: scale(1.02);
  background: rgba(255,255,255,0.1);
}

blockquote {
  max-width: 720px;
  margin: 28px auto;
  padding: 14px 18px;
  border-left: 4px solid var(--accent);
  background: rgba(255,255,255,0.03);
  color: var(--muted);
  font-style: italic;
  border-radius: 6px;
}

.sources {
  max-width: 800px;
  margin: 40px auto;
  text-align: left;
  padding: 20px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 10px;
}

.sources h3 {
  color: var(--accent);
  margin-bottom: 10px;
  text-align: center;
}

.sources ul {
  list-style: none;
  padding: 0;
}

.sources li {
  margin: 6px 0;
}

.sources a {
  color: var(--link-color);
  text-decoration: none;
  font-weight: 500;
}

.sources a:hover {
  color: var(--accent);
  text-decoration: underline;
}

footer {
  padding: 20px;
  color: var(--muted);
  font-size: 0.9rem;
  text-align: center;
  background: rgba(255,255,255,0.02);
}

#night:checked ~ main,
#night:checked ~ footer {
  --bg-gradient: linear-gradient(180deg, #1e2b30, #243946, #1a2630);
  --text-color: #e3f8ff;
  --accent: #90caf9;
  --muted: #a2b8c7;
  --link-color: #a4d4ff;
  --header-bg: rgba(20,28,35,0.95);
  background: var(--bg-gradient);
  color: var(--text-color);
}

#night:checked ~ header {
  background: var(--header-bg);
}

#night:checked ~ header .nav-links a {
  color: var(--link-color);
}

#night:checked ~ header .nav-links a.active {
  background: rgba(255,255,255,0.08);
  color: #fff;
}

@media (max-width: 700px) {
  .nav-links { flex-direction: column; gap: 8px; }
  .mode-switch { top: 66px; right: 12px; }
  .research-img { width: 70%; max-width: 280px; }
  h2 { font-size: 1.3rem; }
}