/* 首页开始按钮：圆形按钮配合阴影与旋转星标制造主 CTA 动效。 */
.a-btn {
    width: 100px;
    height: 100px;
    -webkit-border-radius: 50%;
    -moz-border-radius: 50%;
    border-radius: 50%;
    display: block;
    margin-top: 30px;
    left: 50%;
    margin-left: -50px;
    background: #f0ad4e;
    position: relative;
    -webkit-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px 0px 1px 8px rgba(188, 188, 188, 0.4), 0px 0px 0px 9px #fff;
    -moz-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px 0px 1px 8px rgba(188, 188, 188, 0.4), 0px 0px 0px 9px #fff;
    box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px 0px 1px 8px rgba(188, 188, 188, 0.4), 0px 0px 0px 9px #fff;
    -webkit-transition: all 0.3s linear;
    -moz-transition: all 0.3s linear;
    -o-transition: all 0.3s linear;
    transition: all 0.3s linear;
}

.a-btn span {
    display: table-cell;
    width: 100px;
    height: 100px;
    padding: 20px;
    text-align: center;
    vertical-align: middle;
    font-size: 26px;
    color: #fff;
    text-shadow: 0px 1px 1px #A03F16;
    font-family: "Arvo", "Myriad Pro", "Trebuchet MS", sans-serif;
    -webkit-transition: all 0.3s linear;
    -moz-transition: all 0.3s linear;
    -o-transition: all 0.3s linear;
    transition: all 0.3s linear;
}

.a-btn span:nth-child(1),
.a-btn span:nth-child(3) {
    position: absolute;
    top: 0px;
    left: 0px;
    font-size: 40px;
    line-height: 36px;
    opacity: 0;
}

.a-btn span:nth-child(1) {
    /* 第一层是背景星标，只在 hover 时转动并加强视觉反馈。 */
    background: transparent url(/static/img/star.png) no-repeat center center;
    opacity: 0.2;
}

.a-btn:hover {
    text-decoration: none;
    background: rgba(170, 77, 27, 0.6);
    -webkit-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 1px 4px 5px 8px rgba(188, 188, 188, 0.6), 0px 0px 0px 9px #fff;
    -moz-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 1px 4px 5px 8px rgba(188, 188, 188, 0.6), 0px 0px 0px 9px #fff;
    box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 1px 4px 5px 8px rgba(188, 188, 188, 0.6), 0px 0px 0px 9px #fff;
}

.a-btn:hover span:nth-child(3) {
    margin-top: 10px;
    opacity: 1;
}

.a-btn:hover span:nth-child(2) {
    opacity: 0;
    -webkit-transform: scale(0);
    -moz-transform: scale(0);
    transform: scale(0);
}

.a-btn:hover span:nth-child(1) {
    -webkit-animation: rotate 1s linear;
    -moz-animation: rotate 1s linear;
    animation: rotate 1s linear;
}

.a-btn:active {
    -webkit-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px -1px 0px 8px rgba(188, 188, 188, 0.3), 0px 0px 0px 10px #fff;
    -moz-box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px -1px 0px 8px rgba(188, 188, 188, 0.3), 0px 0px 0px 10px #fff;
    box-shadow: 0px 0px 5px 0px rgba(246, 212, 163, 0.5) inset, 0px -1px 5px 4px rgba(170, 77, 27, 0.2) inset, 0px 0px 0px 7px #fff, 0px -1px 0px 8px rgba(188, 188, 188, 0.3), 0px 0px 0px 10px #fff;
}

.a-btn:active span:nth-child(2) {
    color: rgba(170, 77, 27, 0.8);
    text-shadow: 0px 1px 1px rgba(255, 255, 255, 0.6);
}

@keyframes rotate {

    /* 点击前的悬停动画通过缩放加旋转提升“开始测试”的仪式感。 */
    0% {
        transform: scale(1) rotate(0);
    }

    50% {
        transform: scale(0.5) rotate(180deg);
    }

    100% {
        transform: scale(1) rotate(360deg);
    }
}

@-webkit-keyframes rotate {
    0% {
        -webkit-transform: scale(1) rotate(0);
    }

    50% {
        -webkit-transform: scale(0.5) rotate(180deg);
    }

    100% {
        -webkit-transform: scale(1) rotate(360deg);
    }
}

@-moz-keyframes rotate {
    0% {
        -moz-transform: scale(1) rotate(0);
    }

    50% {
        -moz-transform: scale(0.5) rotate(180deg);
    }

    100% {
        -moz-transform: scale(1) rotate(360deg);
    }
}