/* Basic Reset and Font */
:root {
  --primary-color: #2c3e50; /* A dark slate blue */
  --secondary-color: #34495e; /* A slightly lighter blue-gray */
  --accent-color: #3498db; /* A vibrant blue for accents */
  --text-color: #ecf0f1; /* Light gray for text */
  --light-text-color: #bdc3c7; /* Lighter gray for subtext */
  --background-color: #1a232f; /* Dark background */
  --card-background: #232d3a; /* Slightly lighter card background */
  --border-color: #3e5066; /* Border color */
  --footer-color: #151d28; /* Darker footer */
}

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

body {
  font-family: 'Outfit', sans-serif;
  background-color: var(--background-color);
  color: var(--text-color);
  line-height: 1.6;
  padding-top: 80px; /* Space for the fixed header */
}

/* Header */
header {
  background-color: var(--secondary-color);
  color: var(--text-color);
  padding: 1rem 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1000;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.2);
}

.logo-container {
  display: flex;
  align-items: center;
  gap: 10px;
}

.logo-container img {
  height: 40px;
  border-radius: 50%;
}

.logo-text {
  font-weight: 600;
  margin: 0;
  font-size: 1.5rem;
}

.nav-buttons {
  display: flex;
  gap: 10px;
}

.nav-button {
  background-color: transparent;
  color: var(--text-color);
  border: 2px solid var(--accent-color);
  border-radius: 8px;
  padding: 10px 20px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s ease;
}

.nav-button:hover {
  background-color: var(--accent-color);
  color: var(--primary-color);
  transform: translateY(-2px);
  box-shadow: 0 4px 10px rgba(52, 152, 219, 0.3);
}

.nav-button.active {
  background-color: var(--accent-color);
  color: var(--primary-color);
}

/* Main Content Wrapper */
.content-wrapper {
  padding: 2rem;
  max-width: 900px;
  margin: auto;
}

.container, .about-section {
  display: none;
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.container.active, .about-section.active {
  display: block;
  opacity: 1;
  transform: translateY(0);
}

/* Main Titles and Subheadings */
h1 {
  font-size: 2.5rem;
  text-align: center;
  margin-bottom: 0.5rem;
  color: var(--accent-color);
  animation: slideIn 0.8s ease-out;
}

.subheading {
  font-size: 1.2rem;
  text-align: center;
  color: var(--light-text-color);
  margin-bottom: 2rem;
}

h2 {
  font-size: 2rem;
  margin-top: 2rem;
  margin-bottom: 1.5rem;
  color: var(--accent-color);
  text-align: center;
}

/* Year Selection */
.year-buttons {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin-bottom: 2rem;
}

/* Subject and Unit Sections */
.year-section {
  display: none;
  animation: fadeIn 0.8s ease-in-out;
}

.year-section.active {
  display: block;
}

.subject-card-container {
  display: grid;
  gap: 1.5rem;
}

.subject-card {
  background-color: var(--card-background);
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
  transition: transform 0.3s ease;
}

.subject-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
}

.subject-btn {
  width: 100%;
  background-color: var(--secondary-color);
  color: var(--text-color);
  border: none;
  padding: 18px 25px;
  font-size: 1.2rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  transition: background-color 0.3s ease, border-radius 0.3s ease;
}

.subject-btn:hover {
  background-color: var(--primary-color);
}

.subject-btn.active {
  background-color: var(--accent-color);
  color: var(--primary-color);
  border-bottom-left-radius: 0;
  border-bottom-right-radius: 0;
}

.subject-btn .icon {
  font-size: 1rem;
  transition: transform 0.3s ease;
}

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

.units-container {
  padding: 0 15px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.4s ease-out;
  background-color: var(--card-background);
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
  gap: 10px;
}

.units-container.expanded {
  max-height: 500px; /* A large value to allow for expansion */
  padding: 15px;
}

.unit-box {
  background-color: var(--primary-color);
  border-radius: 8px;
  text-align: center;
  transition: background-color 0.3s ease, transform 0.2s ease;
}

.unit-box:hover {
  background-color: var(--accent-color);
  transform: translateY(-2px);
}

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

.unit-link {
  display: block;
  padding: 12px;
  color: var(--text-color);
  text-decoration: none;
  font-weight: 600;
  transition: color 0.3s ease;
}

/* About Section */
.about-section {
  padding-top: 2rem;
  text-align: center;
}

.about-card {
  background-color: var(--card-background);
  padding: 2.5rem;
  border-radius: 12px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.about-card p {
  margin-bottom: 1rem;
  font-size: 1.1rem;
}

.contact-list {
  list-style: none;
  padding: 0;
  margin-top: 1.5rem;
}

.contact-list li {
  margin-bottom: 0.8rem;
}

.contact-list a {
  color: var(--accent-color);
  text-decoration: none;
  font-weight: 600;
  transition: color 0.3s ease;
}

.contact-list a:hover {
  color: #5cd3ff;
  text-decoration: underline;
}

/* Footer */
footer {
  background-color: var(--footer-color);
  color: var(--light-text-color);
  text-align: center;
  padding: 1rem;
  margin-top: 3rem;
  font-size: 0.9rem;
}

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

@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

/* Media Queries for Mobile Responsiveness */
@media (max-width: 768px) {
  body {
    padding-top: 70px;
  }

  header {
    flex-direction: column;
    text-align: center;
    padding: 1rem;
    position: static;
  }

  .logo-container {
    flex-direction: column;
    margin-bottom: 1rem;
  }

  .nav-buttons {
    width: 100%;
    justify-content: center;
  }

  .nav-button {
    flex: 1;
    padding: 8px;
    font-size: 0.9rem;
  }
  
  .content-wrapper {
    padding: 1rem;
  }

  h1 {
    font-size: 2rem;
  }

  .subheading {
    font-size: 1rem;
  }
  
  .year-buttons {
    flex-direction: column;
    gap: 1rem;
  }

  .units-container {
    grid-template-columns: 1fr 1fr;
  }

  .about-card {
    padding: 1.5rem;
  }
}

@media (max-width: 480px) {
  .nav-buttons {
    gap: 5px;
  }
  
  .subject-btn {
    font-size: 1rem;
    padding: 15px 20px;
  }

  .unit-box {
    padding: 8px;
  }

  .units-container {
    grid-template-columns: 1fr;
  }
}