:root {
  --ms-blue: #0078d4;
  --ms-dark-blue: #005a9e;
  --ms-light-blue: #deecf9;
  --ms-green: #107c10;
  --ms-yellow: #ffb900;
  --ms-red: #d83b01;
  --ms-purple: #5c2d91;
  --gradient-start: #0078d4;
  --gradient-end: #00bcf2;
  --bg-color: #f5f5f5;
  --card-bg: #ffffff;
  --text-primary: #1a1a1a;
  --text-secondary: #616161;
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
  --shadow-hover: 0 8px 30px rgba(0, 120, 212, 0.2);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Segoe UI', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-color);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
}

header {
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  color: white;
  padding: 3rem 2rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

header::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle, rgba(255,255,255,0.1) 0%, transparent 70%);
  animation: pulse 15s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { transform: scale(1); opacity: 0.5; }
  50% { transform: scale(1.1); opacity: 0.3; }
}

.header-content {
  position: relative;
  z-index: 1;
  max-width: 900px;
  margin: 0 auto;
}

.logo {
  height: 50px;
  margin-bottom: 1.5rem;
  filter: brightness(0) invert(1);
}

h1 {
  font-size: 2.8rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
  text-shadow: 0 2px 10px rgba(0,0,0,0.2);
}

.subtitle {
  font-size: 1.2rem;
  font-weight: 300;
  opacity: 0.95;
  margin-bottom: 0.5rem;
}

.credit {
  font-size: 0.9rem;
  opacity: 0.8;
  font-style: italic;
}

.filter-nav {
  display: flex;
  justify-content: center;
  gap: 0.75rem;
  padding: 1.5rem;
  background: var(--card-bg);
  box-shadow: 0 2px 10px rgba(0,0,0,0.05);
  flex-wrap: wrap;
  position: sticky;
  top: 0;
  z-index: 100;
}

.filter-btn {
  padding: 0.6rem 1.5rem;
  border: 2px solid var(--ms-blue);
  background: transparent;
  color: var(--ms-blue);
  border-radius: 25px;
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 600;
  transition: all 0.3s ease;
}

.filter-btn:hover {
  background: var(--ms-light-blue);
}

.filter-btn.active {
  background: var(--ms-blue);
  color: white;
}

main {
  padding: 3rem 1rem;
  max-width: 1200px;
  margin: 0 auto;
}

.timeline-container {
  position: relative;
  padding: 2rem 0;
}

.timeline-line {
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: 4px;
  background: linear-gradient(180deg, var(--ms-blue), var(--ms-purple), var(--ms-green));
  transform: translateX(-50%);
  border-radius: 2px;
}

.timeline {
  position: relative;
}

.timeline-item {
  display: flex;
  justify-content: flex-end;
  padding-right: calc(50% + 40px);
  position: relative;
  margin-bottom: 3rem;
  opacity: 0;
  transform: translateX(-30px);
  animation: slideInLeft 0.6s ease forwards;
}

.timeline-item:nth-child(even) {
  justify-content: flex-start;
  padding-right: 0;
  padding-left: calc(50% + 40px);
  transform: translateX(30px);
  animation: slideInRight 0.6s ease forwards;
}

@keyframes slideInLeft {
  to { opacity: 1; transform: translateX(0); }
}

@keyframes slideInRight {
  to { opacity: 1; transform: translateX(0); }
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: 50%;
  top: 20px;
  width: 20px;
  height: 20px;
  background: var(--card-bg);
  border: 4px solid var(--ms-blue);
  border-radius: 50%;
  transform: translateX(-50%);
  z-index: 1;
  transition: all 0.3s ease;
}

.timeline-item:hover::before {
  transform: translateX(-50%) scale(1.3);
  background: var(--ms-blue);
}

.timeline-item[data-category="opensource"]::before { border-color: var(--ms-green); }
.timeline-item[data-category="opensource"]:hover::before { background: var(--ms-green); }
.timeline-item[data-category="products"]::before { border-color: var(--ms-purple); }
.timeline-item[data-category="products"]:hover::before { background: var(--ms-purple); }
.timeline-item[data-category="cloud"]::before { border-color: var(--ms-yellow); }
.timeline-item[data-category="cloud"]:hover::before { background: var(--ms-yellow); }
.timeline-item[data-category="foundation"]::before { border-color: var(--ms-red); }
.timeline-item[data-category="foundation"]:hover::before { background: var(--ms-red); }

.timeline-card {
  background: var(--card-bg);
  border-radius: 16px;
  padding: 1.5rem;
  box-shadow: var(--shadow);
  max-width: 450px;
  transition: all 0.3s ease;
  position: relative;
  overflow: hidden;
}

.timeline-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--ms-blue);
}

.timeline-item[data-category="opensource"] .timeline-card::before { background: var(--ms-green); }
.timeline-item[data-category="products"] .timeline-card::before { background: var(--ms-purple); }
.timeline-item[data-category="cloud"] .timeline-card::before { background: var(--ms-yellow); }
.timeline-item[data-category="foundation"] .timeline-card::before { background: var(--ms-red); }

.timeline-card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-hover);
}

.timeline-year {
  display: inline-block;
  background: linear-gradient(135deg, var(--ms-blue), var(--ms-dark-blue));
  color: white;
  padding: 0.3rem 1rem;
  border-radius: 20px;
  font-weight: 700;
  font-size: 0.9rem;
  margin-bottom: 0.75rem;
}

.timeline-item[data-category="opensource"] .timeline-year { 
  background: linear-gradient(135deg, var(--ms-green), #0b5a0b); 
}
.timeline-item[data-category="products"] .timeline-year { 
  background: linear-gradient(135deg, var(--ms-purple), #3c1d61); 
}
.timeline-item[data-category="cloud"] .timeline-year { 
  background: linear-gradient(135deg, var(--ms-yellow), #cc9400); 
}
.timeline-item[data-category="foundation"] .timeline-year { 
  background: linear-gradient(135deg, var(--ms-red), #a52f01); 
}

.timeline-title {
  font-size: 1.3rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.timeline-description {
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.7;
}

.timeline-badge {
  display: inline-block;
  margin-top: 0.75rem;
  padding: 0.2rem 0.75rem;
  background: var(--ms-light-blue);
  color: var(--ms-dark-blue);
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
}

.highlight {
  border: 2px solid var(--ms-blue);
  box-shadow: 0 0 0 4px rgba(0, 120, 212, 0.15);
}

.timeline-item[data-category="opensource"] .highlight {
  border-color: var(--ms-green);
  box-shadow: 0 0 0 4px rgba(16, 124, 16, 0.15);
}

footer {
  text-align: center;
  padding: 2rem;
  background: var(--text-primary);
  color: white;
  font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 768px) {
  .timeline-line {
    left: 20px;
  }
  
  .timeline-item,
  .timeline-item:nth-child(even) {
    justify-content: flex-start;
    padding-left: 60px;
    padding-right: 1rem;
  }
  
  .timeline-item::before,
  .timeline-item:nth-child(even)::before {
    left: 20px;
  }
  
  .timeline-card {
    max-width: 100%;
  }
  
  h1 {
    font-size: 2rem;
  }
  
  .filter-nav {
    gap: 0.5rem;
  }
  
  .filter-btn {
    padding: 0.5rem 1rem;
    font-size: 0.8rem;
  }
}

/* Animation delays for staggered effect */
.timeline-item:nth-child(1) { animation-delay: 0.1s; }
.timeline-item:nth-child(2) { animation-delay: 0.2s; }
.timeline-item:nth-child(3) { animation-delay: 0.3s; }
.timeline-item:nth-child(4) { animation-delay: 0.4s; }
.timeline-item:nth-child(5) { animation-delay: 0.5s; }
.timeline-item:nth-child(6) { animation-delay: 0.6s; }
.timeline-item:nth-child(7) { animation-delay: 0.7s; }
.timeline-item:nth-child(8) { animation-delay: 0.8s; }
.timeline-item:nth-child(9) { animation-delay: 0.9s; }
.timeline-item:nth-child(10) { animation-delay: 1.0s; }