.main_bg{
  background-image: url("https://gakuensai.cloudfree.jp/materials/background/background.png");
  height: 100vh;
}

.title{
  text-align: center;
  font-weight: bold;
  padding-top: 110px;
  font-family: sans-serif;
}

.explanation{
  text-align: center;
  margin: 10px;
  padding-bottom: 100px;
  font-family: sans-serif; 
}