1.父元素中的子元素设置居中效果
display: flex;
align-items: center; /* 上下居中 */
justify-content: center; /* 左右居中 */
例子：
.left {
display: flex;
align-items: center;
width: 50%;
height: 100%;
background: white;
}
.left-logo {
width: 38px;
height: 38px;
background: url(assets/logo.png) 0 0 no-repeat;
background-size: cover;
}
.left-title {
font-size: 24px;
font-weight: 600;
color: #1a66ff;
font-family: 'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;
}
