//HTML





<div class="custom-mouse"></div>





//CSS


.custom-mouse{
    border: none;
    background-color: #fff;
    transform: translate(-50%, -100%);
    width: 20px;
    height: 20px;
    border-radius: 50%;
    position: absolute;
    top: 0;
}



//JS


let customMouse = document.querySelector(".custom-mouse");
window.addEventListener("mousemove", function(details) {
   let xValue = details.clientX;
   let yValue = details.clientY;

   setTimeout(() => {
       customMouse.style.top = `${yValue}px`;
       customMouse.style.left = `${xValue}px`;
         
   }, 100);


});