var checkbox = document.querySelector('input[name=mode]'); checkbox.addEventListener('change', function() { if(this.checked) { trans() document.documentElement.setAttribute('data-theme', 'dark') } else { trans() document.documentElement.setAttribute('data-theme', 'light') } }) let trans = () => { document.documentElement.classList.add('transition'); window.setTimeout(() => { document.documentElement.classList.remove('transition'); }, 1000) }