html元素永远点不到···

function btn_move(el, mouseLeft, mouseTop){
    var leftRnd = (Math.random()-0.5)*20;
    var topRnd = (Math.random()-0.5)*20;
    var btnLeft = mouseLeft+(leftRnd>0?100:-100)+leftRnd;
    var btnTop = mouseTop+(topRnd>0?30:-30)+topRnd;
    btnLeft = btnLeft<100?(btnLeft+window.innerWidth-200):(btnLeft>window.innerWidth-100?btnLeft-window.innerWidth+200:btnLeft);
    btnTop =  btnTop<100?( btnTop+window.innerHeight-200):(btnTop>window.innerHeight-100?btnTop-window.innerHeight+200:btnTop);
    el.style.position = 'fixed';
    el.style.left = btnLeft+'px';
    el.style.top = btnTop+'px';
}

function over_btn(e){
    if(!e){
        e = window.event;
    }
    btn_move(this, e.clientX, e.clientY);
}

document.getElementById('gbqfba').onmouseover = over_btn;