how do i do a case-insensitive search using DOM in JavaScript?

Question

I am in a dilemma and I need help with Javascript. I need to create code that whenever a user enters a word like CHickEN it needs to match chicken. More examples: “CHICKEN”,"ChIcKeN”, “cHICKen” needs to match chicken. How can I achieve this?

document.getElementById('searchBox').addEventListener('keydown', function (event) {

    if (event.which === 13 || event.keyCode === 13) {

        var searchText = this.value;

        var list = document.querySelectorAll('dd, h1, h2, span, dt');
        var list2 = document.querySelectorAll('dd');
        var items = document.querySelectorAll('li');

        for(var i = 0; i < list.length; i++){

            list[i].style.backgroundColor = '';
            list[i].style.diplay = 'none';
            if (list[i].textContent == searchText){
                list[i].style.backgroundColor = 'yellow';
                list[i].ignoreCase;
            } 
        }
    }
});