css動畫效果：鼠標移上去底部線條從中間往四周動畫延伸

css動畫效果：鼠標移上去底部線條從中間往四周動畫延伸

如圖：

.top-nav a:after {
    content: ' ';
    position: absolute;
    z-index: 2;
    bottom: 0;
    left: 50%;
    display: block;
    width: 165px;
    height: 1px;
    transform: translate(-50%);
}

.top-nav a:hover:after {
    height: 2px;
    animation: ad_width .5s linear forwards;
    background: #ff8a00;
}

@keyframes ad_width {
    from {
        width: 0
    }

    to {
        width: 165px
    }
}