const CONSTANT = {
UNASSIGNED: 0,
GRID_SIZE: 9,
BOX_SIZE: 3,
NUMBERS: [1,2,3,4,5,6,7,8,9],
LEVEL_NAME: [
'Easy',
'Medium',

const newGrid = (size) => {
let arr = new Array(size);

for (let i = 0; i < size; i++) {
arr[i] = new Array(size);
}

for (let i = 0; i < Math.pow(size, 2); i++) {

document.querySelector('#dark-mode-toggle').addEventListener('click', () => {
document.body.classList.toggle('dark');
const isDarkMode = document.body.classList.contains('dark');
localStorage.setItem('darkmode', isDarkMode);
// chang mobile status bar color
document.querySelector('meta[name="theme-color"').setAttribute('content', isDarkMode ? '#1a1a2e' : '#fff');
});