/* --- Design refresh: contemporary, accessible, and responsive --- */

:root {
  /* Light, green-forward theme */
  --bg: #f4fbf7;               /* app background */
  --panel: #ffffff;            /* card/panel */
  --panel-alt: #f7fbf9;        /* subtle panel gradient end */
  --text: #102317;             /* primary text */
  --muted: #4c6b59;            /* secondary text */
  --brand: #2f855a;            /* brand primary */
  --brand-600: #2a7f62;        /* hover */
  --brand-700: #246c56;        /* active */
  --accent: #18794e;           /* accent lines/icons */
  --border: rgba(16,35,23,0.12);
  --shadow: 0 8px 28px rgba(16,35,23,0.10);
}

/* Base */
body {
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, "Helvetica Neue", Arial, "Noto Sans", "Apple Color Emoji", "Segoe UI Emoji";
  margin: 0;
  background: radial-gradient(900px 300px at 80% -50px, rgba(47,133,90,0.10), transparent 50%),
              radial-gradient(700px 240px at -10% 0px, rgba(42,127,98,0.08), transparent 55%),
              var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* Header / Hero */
header {
  /* Gradient: from background → green core band → back to background */
  background:
    radial-gradient(900px 280px at 85% -180px, rgba(255,255,255,0.18), transparent 60%),
    linear-gradient(90deg,
      var(--bg) 0%,
      var(--bg) 5%,
      rgba(16,185,129,0.98) 35%,
      rgba(5,150,105,0.98) 50%,
      rgba(16,185,129,0.98) 65%,
      var(--bg) 95%,
      var(--bg) 100%
    );
  color: #ffffff;
  padding: 2.75rem 1.5rem 2rem 1.5rem;
  text-align: center;
  border-bottom: none;
}
header h1 {
  margin: 0 0 0.5rem 0;
  font-size: 2.25rem;
  letter-spacing: 0.2px;
  color: #ffffff;
  text-shadow: 0 1px 2px rgba(0,0,0,0.25);
}
header p {
  margin: 0;
  color: rgba(255,255,255,0.92);
}

/* Layout */
.main-layout {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 1.5rem;
  padding: 2rem 1.25rem;
  max-width: 1200px;
  margin: 0 auto;
}

.image-side {
  grid-column: span 4;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
}

.image-side img {
  width: 100%;
  max-width: 520px;
  border-radius: 14px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}

.caption {
  margin-top: 0.5rem;
  font-size: 0.9rem;
  color: var(--muted);
}

.mission-text {
  grid-column: span 4;
  background: linear-gradient(180deg, var(--panel), var(--panel-alt));
  padding: 2rem;
  border-radius: 14px;
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}

.mission-text h2 {
  color: var(--text);
  margin-top: 0;
}

.mission-text p {
  color: var(--muted);
  line-height: 1.6;
}

/* Buttons */
.explorer-button-container { text-align: center; margin: 1.75rem 0 0; }
.explorer-button {
  display: inline-block;
  background: linear-gradient(180deg, var(--brand), var(--brand-600));
  color: #fff;
  padding: 0.85em 1.6em;
  text-decoration: none;
  border-radius: 10px;
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: 0.2px;
  border: 1px solid rgba(255,255,255,0.12);
  box-shadow: 0 8px 24px rgba(42,127,98,0.25);
}
.explorer-button:hover { background: linear-gradient(180deg, var(--brand-600), var(--brand-700)); }

/* Footer */
footer {
  text-align: center;
  padding: 1.75rem 1rem;
  background: #ffffff;
  color: var(--muted);
  font-size: 0.95rem;
  border-top: 1px solid var(--border);
}
footer a { color: var(--accent); text-decoration: none; }
footer a:hover { text-decoration: underline; }

/* Timeline Explorer shared elements */
.overview-section, .timeline-section, .example-list {
  background: linear-gradient(180deg, var(--panel), var(--panel-alt));
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: var(--shadow);
}
.overview-section { padding: 1.5rem; margin: 1.5rem auto; max-width: 1200px; }
.timeline-section { padding: 1.25rem; margin: 1.5rem auto; max-width: 1200px; }
.example-list { padding: 1rem; margin-top: 1rem; }
.timeline-section h2, .overview-section h2 { margin-top: 0; }
.back-button-container { max-width: 1200px; margin: 0 auto 1rem auto; padding: 0 1.25rem; }
.back-button {
  display: inline-block; padding: 8px 14px; background: #eef7f1; color: var(--text);
  text-decoration: none; border-radius: 8px; border: 1px solid var(--border);
}
.back-button:hover { background: #e6f3ea; }

/* Links */
a { color: var(--brand-700); }
a:hover { color: var(--brand); }

/* Responsive */
@media (max-width: 1100px) {
  .image-side { grid-column: span 6; }
  .mission-text { grid-column: span 12; }
}
@media (max-width: 720px) {
  header h1 { font-size: 1.9rem; }
  .main-layout { grid-template-columns: repeat(6, 1fr); }
  .image-side, .mission-text { grid-column: span 6; }
}