<style>

div{

    background-image: url('/static/i/javascript/basic/img_tree.png');

    background-repeat: no-repeat;

    width: 400px;

    height: 400px;

    border: 1px solid #000000;

}

</style>

<script>

function displayResult(){

    document.getElementById("div1").style.backgroundPosition="center bottom"; 

}

</script>

<button type="button" onclick="displayResult()">修改背景图像位置</button>

<br>

<div id="div1">

</div>