<style>
.none{display: none}
#toolbar {
display: flex;
justify-content: center;
align-items: center;
position: fixed;
max-width: 100%;
left: 0;
/*top:0; */ /*置顶*/
bottom: 0px; /*置底*/
margin: auto;
}
</style>
导航那段HTML 外面加 div标签，id=“toolbar” 。完毕