How to add ID element to webflow DIV?

Design help Custom code
1

hello, i have problem with slider. This code: ( i cant get element by id ‘next’ bcs i cant add ID data to DIV

//step 1: get DOM
let nextDom = document.getElementByID('next');
let prevDom = document.getElementByID('prev');

let carouselDom = document.querySelector('.carousel');
let SliderDom = carouselDom.querySelector('.carousel .list');
let thumbnailBorderDom = document.querySelector('.carousel .thumbnail');
let thumbnailItemsDom = thumbnailBorderDom.querySelectorAll('.item');
let timeDom = document.querySelector('.carousel .time');

thumbnailBorderDom.appendChild(thumbnailItemsDom[0]);
let timeRunning = 3000;
let timeAutoNext = 7000;

nextDom.onclick = function(){
    showSlider('next');    
}

prevDom.onclick = function(){
    showSlider('prev');    
}
let runTimeOut;
let runNextAuto = setTimeout(() => {
    next.click();
}, timeAutoNext)
function showSlider(type){
    let  SliderItemsDom = SliderDom.querySelectorAll('.carousel .list .item');
    let thumbnailItemsDom = document.querySelectorAll('.carousel .thumbnail .item');
    
    if(type === 'next'){
        SliderDom.appendChild(SliderItemsDom[0]);
        thumbnailBorderDom.appendChild(thumbnailItemsDom[0]);
        carouselDom.classList.add('next');
    }else{
        SliderDom.prepend(SliderItemsDom[SliderItemsDom.length - 1]);
        thumbnailBorderDom.prepend(thumbnailItemsDom[thumbnailItemsDom.length - 1]);
        carouselDom.classList.add('prev');
    }
    clearTimeout(runTimeOut);
    runTimeOut = setTimeout(() => {
        carouselDom.classList.remove('next');
        carouselDom.classList.remove('prev');
    }, timeRunning);

    clearTimeout(runNextAuto);
    runNextAuto = setTimeout(() => {
        next.click();
    }, timeAutoNext)
}

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2

The image below shows where to add the ID for an element and me doing so.

image (9)
image (9)1005×857 62.1 KB

I did not look at your code.