* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont;
  background: #f5f6fa;
}
header {
  display: flex;
  justify-content: space-between;
  padding: 12px 16px;
  background: #1e90ff;
  color: #fff;
}
button {
  padding: 6px 12px;
  border: none;
  border-radius: 4px;
  background: #fff;
  cursor: pointer;
}
main {
  padding: 12px;
}
.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit,minmax(120px,1fr));
  gap: 12px;
}
.card {
  background: #fff;
  padding: 16px;
  border-radius: 6px;
  text-align: center;
  cursor: pointer;
}
.roster {
  display: grid;
  grid-template-columns: repeat(auto-fit,minmax(140px,1fr));
  gap: 8px;
}
.group {
  background: #fff;
  border-radius: 6px;
  padding: 8px;
}
.student {
  display: flex;
  justify-content: space-between;
  padding: 4px 0;
}
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.4);
}
.modal-content {
  background: #fff;
  padding: 16px;
  max-width: 320px;
  margin: 20vh auto;
  border-radius: 6px;
}
.hidden { display: none; }