/* ============================================
   RESEARCH TIMELINE SECTION
   ============================================ */

.timeline {
  position: relative;
  padding: var(--space-8) 0;
}

.timeline::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 3px;
  height: 100%;
  background: linear-gradient(
    to bottom,
    var(--color-primary),
    var(--color-accent),
    var(--color-secondary)
  );
  border-radius: var(--radius-full);
}

.timeline__item {
  display: flex;
  align-items: flex-start;
  margin-bottom: var(--space-12);
  position: relative;
}

.timeline__item:nth-child(odd) {
  flex-direction: row;
  padding-right: calc(50% + 30px);
}

.timeline__item:nth-child(even) {
  flex-direction: row-reverse;
  padding-left: calc(50% + 30px);
}

.timeline__dot {
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  width: 16px;
  height: 16px;
  background: var(--color-accent);
  border: 3px solid var(--color-white);
  border-radius: 50%;
  box-shadow: 0 0 0 4px rgba(var(--color-accent-rgb), 0.2);
  z-index: 2;
}

.timeline__content {
  background: var(--color-white);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--color-gray-200);
  width: 100%;
  transition: all var(--transition-base);
}

.timeline__content:hover {
  box-shadow: var(--shadow-xl);
}

.timeline__date {
  font-size: var(--text-sm);
  font-weight: var(--font-weight-bold);
  color: var(--color-accent);
  font-family: var(--font-mono);
  margin-bottom: var(--space-2);
}

.timeline__title {
  font-size: var(--text-lg);
  margin-bottom: var(--space-2);
}

.timeline__description {
  font-size: var(--text-sm);
  color: var(--text-muted);
  line-height: var(--line-height-relaxed);
  margin-bottom: 0;
}

.timeline__tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-3);
}

@media (max-width: 768px) {
  .timeline::before {
    left: 20px;
  }

  .timeline__item:nth-child(odd),
  .timeline__item:nth-child(even) {
    flex-direction: row;
    padding-left: 50px;
    padding-right: 0;
  }

  .timeline__dot {
    left: 20px;
  }
}