DIVのピントずれ（ぼかし）実装方法

    /**
     *Mouseover div event
     */
    function moveOverEvent(ele,outTimer) {
        let overTimer = null;
        return function(){
            clearTimeout(outTimer); //div is not gone in the case of moving in the div, then clear the last move out event
            clearTimeout(overTimer); //anti-jitter
            overTimer = setTimeout(()=>{        
                ele.style.display = "block";
            },500);                     
        }
    }
    /**
     * mouseover
     */
    function moveOutEvent(ele,outTimer) {
        return function(){
            clearTimeout(outTimer); // anti-shake
            outTimer = setTimeout(()=>{ //wait 500ms after moving out, before disappearing this div
                ele.style.display = "none";
            },500);
        }
    }

//After tabindex is set, the element is dashed by default and removed by outline=0 (IE sets hidefocus="true")
<div tabindex="0" outline=0" hidefocus="true"></div>