#sub_ct {
  max-width: 900px;
  margin: 20px auto 40px;
}

#sub_ct ul{
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

#sub_ct ul>li{
  margin: 0 5px 10px;
  width: calc( ( 100% - 30px ) / 2 );
}

@media screen and (min-width: 900px){
  #sub_ct ul>li{
    width: calc( ( 100% - 80px ) / 4 );
  }
}

#sub_ct ul a{
  display: block;
  text-decoration: none;
  padding: .5em 1em;
  background: #000;
  color: #fff;
  text-align: center;
  opacity: 1;
}