@media screen and (min-width:640px){
 /* for PC*/
 table.tbbook{
  margin-left: auto;
  margin-right: auto;
  width:500px;
 }

}

@media screen and (max-width:640px){
/* for smart phone or Tablet device*/

 table.tbbook{
  margin-left: auto;
  margin-right: auto;
  width:95vw;
  max-width:500px;
 }
}

ul.content li{
  margin-top:0.5em; 
  margin-bottom:0.5em;
}