html,body{
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
}
input{
  display: block;
  width: 80%;
  font-family: Helvetica;
  font-size: 2em;
  margin: 0 auto 0.3em;
}
#btn{
  display: inline-block;
  width: 60%;
  margin: 0 0 0 10%;
}
#cls{
  display: inline-block;
  width: 18%;
}
.table{
  display: table;
  width: 100%;
  height: 100%;
}
.cell{
  display: table-cell;
  vertical-align: middle;
}