Scrolling Timeline

<div class="timeline-container">
  <div class="timeline">
    <div class="timeline-line"></div>
    
    <div class="timeline-item">
      <div class="timeline-dot"></div>
      <div class="timeline-content">
        <div class="timeline-date">2023</div>
        <h3>First Event</h3>
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
      </div>
    </div>
    
    <div class="timeline-item">
      <div class="timeline-dot"></div>
      <div class="timeline-content">
        <div class="timeline-date">2024</div>
        <h3>Second Event</h3>
        <p>Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</p>
      </div>
    </div>
    
    <div class="timeline-item">
      <div class="timeline-dot"></div>
      <div class="timeline-content">
        <div class="timeline-date">2025</div>
        <h3>Third Event</h3>
        <p>Ut enim ad minim veniam, quis nostrud exercitation ullamco.</p>
      </div>
    </div>
  </div>
</div>

.timeline-container {
  max-width: 800px;
  margin: 0 auto;
  padding: 40px 20px;
}

.timeline {
  position: relative;
}

.timeline-line {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 20px;
  width: 4px;
  background: linear-gradient(to bottom, #6a11cb, #2575fc);
  transform-origin: top center;
  transform: scaleY(0);
  animation: grow-line 1.5s ease forwards;
}

.timeline-item {
  position: relative;
  padding-left: 60px;
  margin-bottom: 50px;
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.timeline-item.active {
  opacity: 1;
  transform: translateY(0);
}

.timeline-dot {
  position: absolute;
  left: 12px;
  top: 5px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: white;
  border: 4px solid #6a11cb;
  box-shadow: 0 0 0 4px rgba(106, 17, 203, 0.2);
  transform: scale(0);
  transition: transform 0.3s ease 0.5s;
}

.timeline-item.active .timeline-dot {
  transform: scale(1);
}

.timeline-content {
  background-color: #fff;
  padding: 20px;
  border-radius: 8px;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
  position: relative;
}

.timeline-content::before {
  content: '';
  position: absolute;
  left: -10px;
  top: 15px;
  width: 0;
  height: 0;
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent;
  border-right: 10px solid #fff;
}

.timeline-date {
  display: inline-block;
  padding: 4px 12px;
  background: linear-gradient(135deg, #6a11cb, #2575fc);
  color: white;
  border-radius: 20px;
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 10px;
}

.timeline-content h3 {
  margin: 0 0 10px;
  color: #333;
  font-size: 18px;
}

.timeline-content p {
  margin: 0;
  color: #666;
  line-height: 1.5;
}

@keyframes grow-line {
  from {
    transform: scaleY(0);
  }
  to {
    transform: scaleY(1);
  }
}

/* Optional control buttons */
.timeline-controls {
  display: flex;
  justify-content: center;
  gap: 15px;
  margin-top: 20px;
}

.timeline-btn {
  padding: 8px 16px;
  background: linear-gradient(135deg, #6a11cb, #2575fc);
  color: white;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  font-weight: 500;
  transition: all 0.2s ease;
}

.timeline-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

/* Responsive styles */
@media (min-width: 768px) {
  .timeline-line {
    left: 50%;
    margin-left: -2px;
  }
  
  .timeline-item {
    padding-left: 0;
    width: 50%;
  }
  
  .timeline-item:nth-child(odd) {
    padding-right: 40px;
    margin-left: 0;
    margin-right: auto;
    text-align: right;
  }
  
  .timeline-item:nth-child(even) {
    padding-left: 40px;
    margin-left: auto;
    margin-right: 0;
  }
  
  .timeline-dot {
    left: auto;
    right: -14px;
  }
  
  .timeline-item:nth-child(even) .timeline-dot {
    right: auto;
    left: -14px;
  }
  
  .timeline-item:nth-child(odd) .timeline-content::before {
    left: auto;
    right: -10px;
    border-right: none;
    border-left: 10px solid #fff;
  }
}

/* Dark mode styles */
@media (prefers-color-scheme: dark) {
  .timeline-content {
    background-color: #2a2a2a;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
  }
  
  .timeline-content::before {
    border-right-color: #2a2a2a;
  }
  
  .timeline-item:nth-child(odd) .timeline-content::before {
    border-left-color: #2a2a2a;
  }
  
  .timeline-dot {
    background: #333;
    border-color: #8a3eff;
    box-shadow: 0 0 0 4px rgba(138, 62, 255, 0.2);
  }
  
  .timeline-date {
    background: linear-gradient(135deg, #8a3eff, #3a7bd5);
  }
  
  .timeline-content h3 {
    color: #eee;
  }
  
  .timeline-content p {
    color: #bbb;
  }
  
  .timeline-line {
    background: linear-gradient(to bottom, #8a3eff, #3a7bd5);
  }
  
  .timeline-btn {
    background: linear-gradient(135deg, #8a3eff, #3a7bd5);
  }
}

/**
 * Initialize the scrolling timeline
 */
function initTimeline() {
  // All timeline items
  const timelineItems = document.querySelectorAll('.timeline-item');
  
  // Optional control buttons
  const showAllBtn = document.querySelector('.show-all-btn');
  const resetBtn = document.querySelector('.reset-btn');
  
  /**
   * Check if an element is in the viewport
   * @param {HTMLElement} element - The element to check
   * @returns {boolean} - Whether the element is in viewport
   */
  function isInViewport(element) {
    const rect = element.getBoundingClientRect();
    return (
      rect.top <= (window.innerHeight || document.documentElement.clientHeight) * 0.8 &&
      rect.bottom >= 0
    );
  }
  
  /**
   * Handle scroll event to reveal timeline items
   */
  function onScroll() {
    timelineItems.forEach(item => {
      if (isInViewport(item)) {
        item.classList.add('active');
      }
    });
  }
  
  /**
   * Show all timeline items immediately
   */
  function showAllItems() {
    timelineItems.forEach((item, index) => {
      // Stagger the animations slightly
      setTimeout(() => {
        item.classList.add('active');
      }, index * 300);
    });
  }
  
  /**
   * Reset all timeline items to hidden state
   */
  function resetItems() {
    timelineItems.forEach(item => {
      item.classList.remove('active');
    });
    
    // Activate the first item after a short delay
    setTimeout(() => {
      if (timelineItems.length > 0) {
        timelineItems[0].classList.add('active');
      }
    }, 300);
  }
  
  // Add scroll event listener
  window.addEventListener('scroll', onScroll);
  
  // Initial check on page load
  window.addEventListener('load', onScroll);
  
  // Add event listeners to control buttons if they exist
  if (showAllBtn) {
    showAllBtn.addEventListener('click', showAllItems);
  }
  
  if (resetBtn) {
    resetBtn.addEventListener('click', resetItems);
  }
}

// Initialize when the DOM is ready
document.addEventListener('DOMContentLoaded', initTimeline);