index.css

@media (max-width: 600px) {
  #main-img {
    width: 100%;	
  }
}

@media (min-width: 600px) {
  #main-img {
    width: 600px;
    margin-left: auto;
    margin-right: auto;
    display: block;
  }
  ul {
    width: 600px;
  }
}

ul {
  margin-left: auto;
  margin-right: auto;
    padding-left: 0px;
}

li {
  list-style: none;
  height: 50px;
  text-align: center;
  text-width: center;
  background: linear-gradient(to right, #2773B0, #FFFFFF);
  border: 3px solid #CCCCCC;
  border-radius: 10px;
  margin: 20px;
  display: flex;
  align-items: center;
  padding-left: 10px;
}

li a {
  text-decoration: none;
  color: white;
  font-size: 30px;
  font-family: sans-serif;
}

address {
  text-align: center;
  color: #666666;
  font-style: normal;
}

address a {
  color: #666666;
}

#kibousoft-viav6 {
  display: block;
  margin-left: auto;
  margin-right: auto;
  width: 50px;
  margin-top: 10px;
}