:root {
  --sim-width: 1280px;
  --sim-height: 720px;
  --card-gap: 2.5rem;
  --font-size: 1.6rem;

  --bg: #ffffff;
  --card-bg: #cdcdcd;
  --text: #070101;
  --text-light: #6b6b6b;
  --accent: #0a2540;
}

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

body {
  background-color: var(--bg);
  color: var(--text);
  font-family: 'Roboto', 'Arial', sans-serif;
  font-size: var(--font-size);
  user-select: none;
  overflow-x: hidden;
}

#main-container {
  padding: 2rem;
  max-width: 1920px;
  margin: 0 auto;
}

h1 {
  margin-bottom: 1.5rem;
  font-size: 2.5rem;
  text-align: center;
  color: var(--text);
  font-weight: 700;
}

.back-btn {
  display: inline-block;
  margin-bottom: 1rem;
  padding: 0.5rem 1.2rem;
  background: var(--accent);
  color: #ffffff;
  border: none;
  border-radius: 8px;
  font-size: 1.2rem;
  cursor: pointer;
  font-weight: bold;
}

.back-btn:hover {
  opacity: 0.85;
}

/* Card Grid */
.card-grid {
  display: flex;
  flex-wrap: wrap;
  gap: var(--card-gap);
  justify-content: center;
}

/* Default Card - For Subjects & Topics (Centered Icon Style) */
.card {
  background: var(--card-bg);
  border-radius: 5px;
  /* overflow: hidden; */
  width: 320px;
  cursor: pointer;
}

.card img {
  width: 120px;
  height: 120px;
  object-fit: contain;
  display: block;
  margin: 3rem auto 1rem auto;
  padding: 2rem;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.3);
}

.card h3 {
  padding: 0 1.2rem 2rem 1.2rem;
  text-align: center;
  font-weight: 600;
  font-size: 1.4rem;
  color: var(--text);
}

.simulation-card,
#content-grid .card,
#sims-grid .card {
  width: 300px;
}

.simulation-card img,
#content-grid .card img,
#sims-grid .card img {
  width: 100%;
  height: 200px;
  object-fit: cover;
  background: #e8e8e8;
  margin: 0;
  padding: 0;
  border-radius: 0;
}

.simulation-card h3,
#content-grid .card h3,
#sims-grid .card h3 {
  padding: 1.2rem;
  text-align: center;
  font-size: 1.35rem;
}

/* Simulation specific hover */
.simulation-card:hover,
#content-grid .card:hover {
  transform: translateY(-8px);
}

.sim-wrapper {
  display: flex;
  justify-content: center;
  align-items: center;
  /* min-height: calc(100vh - 8rem); */
  padding: 2rem 0;
}

#sim-frame {
  width: 100%;
  max-width: var(--sim-width);
  height: var(--sim-height);
  border: none;
  border-radius: 12px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
  background: #000;
  transition: opacity 0.3s ease;
}

@media (max-width: 1400px) {
  #sim-frame {
    max-width: 90vw;
    height: calc(90vw * 9 / 16);
  }
}

@media (max-width: 768px) {
  #sim-frame {
    max-width: 95vw;
    height: calc(95vw * 9 / 16);
  }

  .sim-wrapper {
    min-height: calc(100vh - 6rem);
    padding: 1rem 0;
  }
}