body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: white;
}

.flex-container {
  display: flex;
  justify-content: center; /* center horizontally */
  gap: 10px; /* space between links */
}

.flex-container a {
  color: #2c3e50;
  text-decoration: none;
  font-weight: bold;
  padding: 8px 12px;
  border-radius: 4px;
  transition: background-color 0.3s;
}

.flex-container a:hover {
  background-color: #2c3e50;
}


/* Navbar */
header {
  background: #2c3e50;
  color: white;
  padding: 15px;
  text-align: center;
}
nav {
  display: flex;
  justify-content: center;
  background: #34495e;
  flex-wrap: wrap;
}
nav a {
  color: white;
  padding: 14px 20px;
  text-decoration: none;
  display: block;
}
nav a:hover {
  background: #1abc9c;
}


/* Hero */
.hero {
  text-align: center;
  padding: 60px 20px;
  background: url('https://picsum.photos/1200/500') center/cover no-repeat;
  color: white;
}
.hero h1 {
  font-size: 3em;
  margin: 0;
  background: rgba(0,0,0,0.6);
  display: inline-block;
  padding: 10px 20px;
  border-radius: 8px;
}
.hero p {
  font-size: 1.2em;
  background: rgba(0,0,0,0.5);
  display: inline-block;
  padding: 6px 12px;
  border-radius: 6px;
}

/* Subjects grid */
.subjects {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 15px;
  padding: 20px;
  text-align: center;
}
.subjects a {
  background: #1abc9c;
  color: white;
  padding: 15px;
  text-decoration: none;
  border-radius: 8px;
  transition: background 0.3s;
  display: block;
}
.subjects a:hover {
  background: #16a085;
}

/* Papers grid */
.papers {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 15px;
  padding: 20px;
  text-align: center;
}
.papers a {
  background: #e67e22;
  color: white;
  padding: 12px;
  text-decoration: none;
  border-radius: 8px;
  display: block;
}
.papers a:hover {
  background: #d35400;
}

footer {
  text-align: center;
  padding: 20px;
  background: #2c3e50;
  color: white;
  margin-top: 30px;
}