// 定位全屏
.full-screen {position:absolute;left: 0;top: 0;right: 0;bottom: 0;}

// 定位上下左右居中
.all-center {position: absolute;top: 50%;left: 50%;transform: translate(-50%, -50%);
}

// 定位上下居中.vertical-center {position: absolute;top: 50%;transform: translateY(-50%);}

// 定位左右居中
.horizontal-center {position: absolute;left: 50%;transform: translateX(-50%);
}

// 1px底部边框
.border-1px {position: relative;&:after {display: block;position: absolute;left: 0;bottom: 0;width: 100%;border-top: 1px solid #999;content: '';}
}

或者

// 1px底部边框
.border-1px {position: relative;&:after { content: '';position: absolute;left: 0;right: 0;bottom: 0;height: 1px;background: #999;}
}