<div class="arrow arrow-left-middle">
    arrow-left-middle
</div>
<div class="arrow arrow-left-top">
    arrow-left-top
</div>
<div class="arrow arrow-left-bottom">
    arrow-left-bottom
</div>
<div class="arrow arrow-left-middle-move">
    arrow-left-middle-move
</div>
<div class="arrow arrow-left-top-move">
    arrow-left-top-move
</div>
<div class="arrow arrow-left-bottom-move">
    arrow-left-bottom-move
</div>

.arrow{
    box-sizing: content-box;
    border: 0;
    margin:10px 0.5em;
    cursor: pointer;
    box-sizing: border-box;
    display: inline-block;
    color: #09f;
    background: white;
    padding: 10px 20px;
    text-align: center;
    /* 设置相对定位 */
    position: relative;
    transition: all 0.3s;
    /* 设置层次 会被before after在上面 */
    z-index:1;
}

/* 设置位置和border的颜色-需要与 4(4面) * 3(上中下) * 2(移动) = 24 */
.arrow-left-top:before,
.arrow-left-top-move:before,
.arrow-left-middle:before,
.arrow-left-middle-move:before,
.arrow-left-bottom:before,
.arrow-left-bottom-move:before{
    transition: all 0.3s;
    content: ‘‘;
    border-style: solid;
    width:0;
    height:0;
    display: block;
    position: absolute;
    margin:auto;
}

.arrow-left-top:before,
.arrow-left-top-move:before,
.arrow-left-middle:before,
.arrow-left-middle-move:before,
.arrow-left-bottom:before,
.arrow-left-bottom-move:before{
    border-width:0.5em 0.5em 0.5em 0;
    border-color:transparent white transparent transparent;
}

/* 中间 */
.arrow-left-middle-move:before,
.arrow-left-middle:before{
    /* top 与 bottom 都为0 就会在中间 margin:auto; */
    top:0;
    bottom: 0;
    left:0;
}

/*顶部*/
.arrow-left-top:before,
.arrow-left-top-move:before{
    top: 0;
    left:0;
}

/*底部*/
.arrow-left-bottom:before,
.arrow-left-bottom-move:before{
    bottom: 0;
    left:0;
}


.arrow-left-middle-move:hover:before,
.arrow-left-top-move:hover:before,
.arrow-left-bottom-move:hover:before,
.arrow-left-middle:hover:before,
.arrow-right-middle-move:hover,
.arrow-left-top:hover:before,
.arrow-right-top-move:hover,
.arrow-right-bottom-move:hover,
.arrow-left-bottom:hover:before{
    transform: translateX(-0.5em);
}

.arrow-right-middle-move:hover:before,
.arrow-right-top-move:hover:before,
.arrow-right-bottom-move:hover:before,
.arrow-right-middle:hover:before,
.arrow-left-middle-move:hover,
.arrow-right-top:hover:before,
.arrow-left-top-move:hover,
.arrow-left-bottom-move:hover,
.arrow-right-bottom:hover:before{
    transform: translateX(0.5em);
}