/* ========== RESET & GLOBAL ========== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  font-family: 'Poppins', sans-serif;
  background: #f5f7fa;
  color: #333;
  scroll-behavior: smooth;
}
a {
  text-decoration: none;
  color: inherit;
}

/* ========== NAVBAR ========== */
nav {
  background: #1e1e2f;
  padding: 20px 40px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 999;
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
}
nav h1 {
  color: #00d8ff;
  font-size: 1.8em;
  font-weight: 700;
}
nav ul {
  list-style: none;
  display: flex;
  gap: 30px;
}
nav ul li a {
  color: #fff;
  text-decoration: none;
  font-weight: 500;
  padding: 8px 12px;
  border-radius: 5px;
  transition: all 0.3s ease;
}
nav ul li a:hover {
  background: #00d8ff;
  color: #1e1e2f;
}

/* ========== MAIN SECTION ========== */
.topics-main {
  padding: 60px 40px;
  background: #eef2f7;
  text-align: center;
}
.topics-main h2 {
  font-size: 2em;
  margin-bottom: 40px;
  color: #2c3e50;
}

/* ========== CATEGORY CARDS ========== */
.category-container {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 25px;
  margin-bottom: 50px;
}
.category-card {
  background: linear-gradient(to right, #00d2ff, #3a7bd5);
  color: white;
  padding: 25px 35px;
  font-size: 1.2em;
  font-weight: 600;
  border-radius: 12px;
  cursor: pointer;
  transition: all 0.3s ease;
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.1);
}
.category-card:hover {
  background: linear-gradient(to right, #3a7bd5, #00d2ff);
  transform: translateY(-5px);
}

/* ========== TOPICS DISPLAY ========== */
.topics-container {
  text-align: left;
  max-width: 800px;
  margin: 0 auto;
}
.topics-container h3 {
  font-size: 1.6em;
  margin-bottom: 25px;
  color: #2c3e50;
}

/* ========== VERTICAL TOPIC BUTTONS ========== */
.topic-vertical {
  display: flex;
  flex-direction: column;
  gap: 20px;
  margin-top: 30px;
  z-index: 1;
}

.topic-vertical button {
  background: rgba(255, 255, 255, 0.95);
  border: none;
  padding: 15px 25px;
  font-size: 1.05em;
  border-radius: 10px;
  cursor: pointer;
  font-weight: 600;
  color: #2c3e50;
  transition: all 0.3s ease;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
  text-align: left;
}
.topic-vertical button:hover {
  background: #3498db;
  color: white;
  transform: translateX(10px);
}

/* ========== RESPONSIVE ========== */
@media (max-width: 768px) {
  nav {
    flex-direction: column;
    align-items: flex-start;
  }
  .topics-main {
    padding: 40px 20px;
  }
  .category-card {
    font-size: 1em;
    padding: 20px;
  }
  .topic-vertical button {
    font-size: 1em;
    padding: 12px 20px;
  }
}