:root {
  --primary: #1a73e8;
  --secondary: #fbbc05;
  --accent: #34a853;
  --dark: #202124;
  --light: #f8f9fa;
  --text: #3c4043;
  --gradient-blue: linear-gradient(135deg, #1a73e8 0%, #4285f4 100%);
  --gradient-orange: linear-gradient(135deg, #fbbc05 0%, #f9ab00 100%);
  --shadow-sm: 0 2px 8px rgba(0,0,0,0.1);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.15);
  --shadow-lg: 0 8px 24px rgba(0,0,0,0.2);
}

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

body {
  font-family: 'Roboto', 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
  color: var(--text);
  background-color: var(--light);
  min-height: 100%;
  display: flex;
  flex-direction: column;
}

.header {
  background: var(--gradient-blue);
  color: white;
  padding: 2rem 0;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.header::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url('https://images.gptkong.com/demo/sample1.png') center/cover no-repeat;
  opacity: 0.1;
  z-index: 0;
}

.header-content {
  position: relative;
  z-index: 1;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 2rem;
  background: white;
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 0;
  z-index: 1000;
}

.nav-logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary);
  text-decoration: none;
  display: flex;
  align-items: center;
}

.nav-logo img {
  height: 40px;
  margin-right: 0.5rem;
}

.nav-menu {
  display: flex;
  list-style: none;
}

.nav-item {
  margin-left: 2rem;
}

.nav-link {
  color: var(--dark);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.3s;
  position: relative;
}

.nav-link:hover {
  color: var(--primary);
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--primary);
  transition: width 0.3s;
}

.nav-link:hover::after {
  width: 100%;
}

.main {
  max-width: 1200px;
  margin: 2rem auto;
  padding: 0 2rem;
  display: grid;
  grid-template-columns: 1fr;
  gap: 3rem;
}

.article {
  background: white;
  border-radius: 12px;
  box-shadow: var(--shadow-sm);
  padding: 2.5rem;
  transition: transform 0.3s, box-shadow 0.3s;
}

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

.article-header {
  margin-bottom: 2rem;
  text-align: center;
}

.article-title {
  font-size: 2.2rem;
  color: var(--dark);
  margin-bottom: 1rem;
  background: var(--gradient-blue);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.article-subtitle {
  font-size: 1.1rem;
  color: var(--primary);
  margin-bottom: 1.5rem;
}

.section {
  margin-bottom: 3rem;
}

.section-title {
  font-size: 1.5rem;
  color: var(--primary);
  margin-bottom: 1.5rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--primary);
  display: inline-block;
}

.section-content {
  margin-bottom: 1.5rem;
}

.image-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem;
  margin: 2rem 0;
}

.image-card {
  border-radius: 8px;
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.3s, box-shadow 0.3s;
}

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

.image-card img {
  width: 100%;
  height: auto;
  display: block;
}

.code-block {
  background: #f6f8fa;
  border-radius: 8px;
  padding: 1.5rem;
  margin: 1.5rem 0;
  overflow-x: auto;
  font-family: 'Courier New', Courier, monospace;
  font-size: 0.9rem;
  line-height: 1.5;
  border-left: 4px solid var(--primary);
}

.code-block pre {
  margin: 0;
}

.highlight {
  background-color: rgba(251, 188, 5, 0.2);
  padding: 0.2rem 0.4rem;
  border-radius: 4px;
}

.footer {
  background: var(--dark);
  color: white;
  padding: 2rem 0;
  text-align: center;
  margin-top: 3rem;
}

.footer-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

.notice {
  background: var(--gradient-orange);
  color: white;
  padding: 1rem;
  border-radius: 8px;
  text-align: center;
  margin: 2rem 0;
  box-shadow: var(--shadow-sm);
}

@media (max-width: 768px) {
  .navbar {
    flex-direction: column;
    padding: 1rem;
  }
  
  .nav-menu {
    margin-top: 1rem;
  }
  
  .nav-item {
    margin: 0 0.5rem;
  }
  
  .article {
    padding: 1.5rem;
  }
  
  .article-title {
    font-size: 1.8rem;
  }
}

@media (max-width: 480px) {
  .image-grid {
    grid-template-columns: 1fr;
  }
  
  .nav-menu {
    flex-direction: column;
    align-items: center;
  }
  
  .nav-item {
    margin: 0.5rem 0;
  }
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.section {
  animation: fadeIn 0.6s ease-out forwards;
}

.section:nth-child(2) { animation-delay: 0.1s; }
.section:nth-child(3) { animation-delay: 0.2s; }
.section:nth-child(4) { animation-delay: 0.3s; }
.section:nth-child(5) { animation-delay: 0.4s; }
.section:nth-child(6) { animation-delay: 0.5s; }
.section:nth-child(7) { animation-delay: 0.6s; }
.section:nth-child(8) { animation-delay: 0.7s; }
.section:nth-child(9) { animation-delay: 0.8s; }
.section:nth-child(10) { animation-delay: 0.9s; }

/* Button styles */
.btn {
  display: inline-block;
  padding: 0.8rem 1.5rem;
  border-radius: 8px;
  font-weight: 500;
  text-decoration: none;
  transition: all 0.3s;
  cursor: pointer;
}

.btn-primary {
  background: var(--primary);
  color: white;
  box-shadow: 0 4px 6px rgba(26, 115, 232, 0.2);
}

.btn-primary:hover {
  background: #1557b0;
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(26, 115, 232, 0.3);
}

.btn-secondary {
  background: var(--secondary);
  color: var(--dark);
  box-shadow: 0 4px 6px rgba(251, 188, 5, 0.2);
}

.btn-secondary:hover {
  background: #e6a800;
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(251, 188, 5, 0.3);
}

/* Tooltip */
.tooltip {
  position: relative;
  display: inline-block;
  border-bottom: 1px dotted var(--text);
}

.tooltip .tooltiptext {
  visibility: hidden;
  width: 200px;
  background-color: var(--dark);
  color: white;
  text-align: center;
  border-radius: 6px;
  padding: 0.5rem;
  position: absolute;
  z-index: 1;
  bottom: 125%;
  left: 50%;
  transform: translateX(-50%);
  opacity: 0;
  transition: opacity 0.3s;
}

.tooltip:hover .tooltiptext {
  visibility: visible;
  opacity: 1;
}

/* Accordion */
.accordion {
  background: white;
  border-radius: 8px;
  box-shadow: var(--shadow-sm);
  margin-bottom: 1rem;
  overflow: hidden;
}

.accordion-header {
  padding: 1rem 1.5rem;
  background: var(--light);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-weight: 500;
}

.accordion-content {
  padding: 0 1.5rem;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease-out;
}

.accordion.active .accordion-content {
  padding: 1rem 1.5rem;
  max-height: 500px;
}

.accordion-icon {
  transition: transform 0.3s;
}

.accordion.active .accordion-icon {
  transform: rotate(180deg);
}