hover时效果从中间向两边扩散

.header .nav > li {
    position: relative;
    display: inline-block;
    margin-right: 20px;
    padding: 0 5px;
    font-size: 16px;
    line-height: 76px;
    border-bottom: 2px solid transparent;
    /* -webkit-transition: all 0.3s ease; */
    -ms-transition: all 0.3s ease;
    -moz-transition: all 0.3s ease;
    /* transition: all 0.3s ease; */
}
.header .nav > li a {
    display: block;
    width: 100%;
    height: 100%;
    color: #222;
}
.header .nav > li:after {
    content: "";
    display: block;
    position: absolute;
     left: 50%;
    -webkit-transform: translateX(-50%) scaleX(0);
    -ms-transform: translateX(-50%) scaleX(0);
    transform: translateX(-50%) scaleX(0);
    bottom: -2px;width: 100%;
    height: 2px;
    background: #3E9AFC;
    -webkit-transition: all 0.3s ease-out;
    -ms-transition: all 0.3s ease-out;
    -moz-transition: all 0.3s ease-out;
    transition: all 0.3s ease-out;
}
.header .nav > li:hover:after {
    -webkit-transform: translateX(-50%) scaleX(1);
    -ms-transform: translateX(-50%) scaleX(1);
    -moz-transform: translateX(-50%) scaleX(1);
    transform: translateX(-50%) scaleX(1);
}

li:before｛

background: radial-gradient(#f1b669 0%, white 60%);

｝

hover时，出现的border边框，从中间向两边扩散