* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    border-spacing: 0;
}

#puzzle{
    width: 450px;
    height: 450px;
}

#puzzle input{
    width: 100%;
    height: 100%;
    text-align: center;
    font-size: 30px;
    width: 50px;
    height: 50px;
    border: 1px silver solid;
}

#puzzle input:nth-child(3n):not(:nth-child(9n)){
    border-right: 3px black solid;
}

#puzzle input:nth-child(19){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(20){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(21){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(22){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(23){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(24){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(25){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(26){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(27){
    border-bottom: 3px black solid;
}

#puzzle input:nth-child(46){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(47){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(48){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(49){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(50){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(51){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(52){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(53){
    border-bottom: 3px black solid;
}
#puzzle input:nth-child(54){
    border-bottom: 3px black solid;
}

input[type="number"]::-webkit-outer-spin-button{
    -webkit-appearance: none;
    margin: 0;
}
input[type="number"]::-webkit-inner-spin-button{
    -webkit-appearance: none;
    margin: 0;
}

#puzzle input.incorrect{
    color: red;
    background-color: rgb(255, 150, 150);
}

#puzzle input.readOnlyCell{
    background-color: rgb(235, 235, 235);
}