style.css

* {
    margin: 0;
    padding: 0;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    text-align: center;
    background: #16222A;
    background: -webkit-linear-gradient(to right, #3A6073, #16222A);
    background: linear-gradient(to right, #3A6073, #16222A);
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    height: 100vh;
}

h1 {
    font-weight: 500;
    color: #fff;
    font-size: 3rem;
}

.sudoku-container {
    margin-top: 20px;
    display: flex;
    justify-content: center;
}

table {
    border-collapse: collapse;
    border: 4px solid gold;
}

.cell {
    width: 40px;
    height: 40px;
    text-align: center;
    font-size: 1.3rem;
    border: 1px solid gold;
    transition: all 0.3s ease-in-out;
    font-weight: bold;
}

table tr:nth-child(3n) td,
table tr:nth-child(3n+3) td {
    border-bottom: 2px solid gold;
}

table td:nth-child(3n) {
    border-right: 2px solid gold;
    /* border-right: 2px solid #000; */
}

input {
    outline: none;
}

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

button {
    margin-top: 20px;
    padding: 10px 20px;
    font-size: 16px;
    background-color: #039be5;
    color: #fff;
    border: none;
    cursor: pointer;
    border-radius: 4px;
    transition: all 0.3s ease;
}

button:hover {
    background-color: #0056b3;
}

.solved {
    background-color: rgb(242, 5, 64);
    /* color: white; */
    transition: all 0.2s ease-in-out;
}