htbl,body{
  overflow:hidden;
}

#demo{
  display: grid;
  place-content: center;
  place-items: center;
  user-select:none;
}

#items{
  display:none;
}

ul{
  display:flex;
  margin:10px 0;
  max-width:100%;
}
li{
  display:inline-block;
  width:80px;
  height:80px;
  line-height:80px;
  font-size:32px;
  font-weight:bold;
  text-align:center;
  border:2px solid #000;
  margin:1px;
  cursor:pointer;
}


li:hover{
  background-color:#eee;
}
li.select{
  border:2px solid #f00;
}
.ok li{
  background-color:#afa;
}

.fixed{
  background-color:#ddd;
}

b{
  display:block;
  margin:8px auto;
}
#btns{
  height:80px;
}
button{
  display:block;
  margin:8px auto;
  padding:24px;
}