/* Main Stylesheet for the PRS Research Lab Website */

/* CSS Variables for Easy Theme Management */
:root {
    --primary-dark: #013A63;
    --primary-medium: #01497C;
    --primary-light: #2A6F97;
    --accent-color: #61A5C2;
    --background-light: #F0F8FF;
    --text-dark: #212529;
    --text-light: #F8F9FA;
    --card-bg: #FFFFFF;
    --border-color: #DEE2E6;
    --shadow: 0 4px 15px rgba(0, 0, 0, 0.08);
  }
  
  body {
    font-family: 'Roboto', sans-serif;
    margin: 0;
    background: var(--background-light);
    color: var(--text-dark);
    line-height: 1.7;
  }
  
  h1, h2, h3, h4 {
    font-family: 'Poppins', sans-serif;
    font-weight: 600;
  }
  
  main {
    padding: 2rem;
    max-width: 1100px;
    margin: auto;
  }
  
  section {
    scroll-margin-top: 100px; /* Offset for sticky nav */
    margin-bottom: 4rem;
  }
  
  h2 {
    text-align: center;
    font-size: 2.5rem;
    color: var(--primary-dark);
    margin-bottom: 2.5rem;
    position: relative;
  }
  
  h2::after {
    content: '';
    display: block;
    width: 80px;
    height: 4px;
    background-color: var(--accent-color);
    margin: 0.5rem auto 0;
    border-radius: 2px;
  }
  
  .content-box {
    background: var(--card-bg);
    padding: 2.5rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
    line-height: 1.8;
    text-align: justify;
  }
  
  /* --- Navigation Bar --- */
  nav {
    background-color: var(--primary-dark);
    padding: 1rem;
    text-align: center;
    box-shadow: 0 2px 5px rgba(0,0,0,0.2);
    position: sticky;
    top: 0;
    z-index: 1000;
  }
  
  nav a {
    color: var(--text-light);
    text-decoration: none;
    margin: 0 0.5rem;
    font-weight: 500;
    padding: 0.5rem 1rem;
    border-radius: 6px;
    transition: background-color 0.3s;
  }
  
  nav a:hover, nav a.active {
    background-color: var(--accent-color);
    color: var(--primary-dark);
  }
  
  /* --- Dropdown Menu --- */
  .dropdown {
    position: relative;
    display: inline-block;
    padding-bottom: 10px;
    margin-bottom: -10px;
  }
  
  .dropdown-content {
    display: none;
    position: absolute;
    background-color: var(--card-bg);
    min-width: 260px;
    box-shadow: 0 8px 16px rgba(0,0,0,0.2);
    z-index: 1;
    border-radius: 6px;
    overflow: hidden;
    margin-top: 0;
    left: 50%;
    transform: translateX(-50%);
  }
  
  .dropdown-content a {
    color: var(--primary-dark);
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
    margin: 0;
    border-radius: 0;
  }
  
  .dropdown-content a:hover {
    background-color: #f1f1f1;
  }
  
  .dropdown:hover .dropdown-content {
    display: block;
  }
  
  .dropbtn {
    background-color: transparent;
    color: white;
    padding: 0.5rem 1rem;
    font-size: 16px;
    font-family: inherit;
    font-weight: 500;
    border: none;
    cursor: pointer;
    border-radius: 6px;
    transition: background-color 0.3s;
  }
  
  .dropdown:hover .dropbtn, .dropbtn.active {
    background-color: var(--accent-color);
    color: var(--primary-dark);
  }
  
  /* --- Research Highlight Cards --- */
  .highlight-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2rem;
    margin-top: 2rem;
  }
  
  .highlight-card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    box-shadow: var(--shadow);
    overflow: hidden;
    display: flex;
    flex-direction: column;
    transition: transform 0.3s, box-shadow 0.3s;
  }
  
  .highlight-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px rgba(0,0,0,0.12);
  }
  
  .highlight-card img {
    width: 100%;
    height: 200px;
    object-fit: contain;
    background-color: #f8f9fa;
    padding: 10px;
    box-sizing: border-box;
  }
  
  .highlight-card-content {
    padding: 1.5rem;
    flex-grow: 1;
    display: flex;
    flex-direction: column;
  }
  
  .highlight-card-content h4 {
    color: var(--primary-dark);
    margin-top: 0;
    margin-bottom: 1rem;
  }
  
  .cta-btn {
    background-color: var(--primary-light);
    color: white;
    padding: 0.6rem 1.5rem;
    font-size: 0.9rem;
    text-decoration: none;
    border-radius: 50px;
    transition: background-color 0.3s;
    display: inline-block;
    text-align: center;
    margin-top: auto;
  }
  
  .cta-btn:hover {
    background-color: var(--primary-dark);
  }
  
  /* --- Footer --- */
  footer {
    background-color: var(--primary-dark);
    color: var(--text-light);
    text-align: center;
    padding: 2rem;
    margin-top: 3rem;
  }