.flex {
    display: -webkit-flex;
    display: flex;
}

.flex-1 {
    -webkit-flex: 1;
    flex: 1;
    min-width: 0;
}

.flex-2 {
    -webkit-flex: 2;
    flex: 2;
    min-width: 0;
}

.flex-grow-1 {
    -webkit-flex-grow: 1;
    flex-grow: 1;
}

.flex-wrap {
    flex-wrap: wrap;
    -webkit-flex-wrap: wrap;
}

.flex-row {
    flex-direction: row;
    /*主轴为水平方向，起点在左端*/
}

.flex-row-reverse {
    flex-direction: row-reverse;
    /*主轴为水平方向，起点在右端*/
}

.flex-col {
    flex-direction: column;
    /*主轴为垂直方向，起点在上沿*/
}

.flex-col-reverse {
    flex-direction: column-reverse;
    /*主轴为垂直方向，起点在下沿*/
}

.flex-left {
    justify-content: flex-start;
    /*左对齐*/
}

.flex-center {
    justify-content: center;
    /*水平居中*/
}

.flex-right {
    justify-content: flex-end;
    /*右对齐*/
}

.flex-between {
    justify-content: space-between;
    /*两端对齐，项目之间的间隔都相等*/
}

.flex-around {
    justify-content: space-around;
    /*每个项目两侧的间隔相等。所以，项目之间的间隔比项目与边框的间隔大一倍*/
}

.align-items-stretch {
    align-items: stretch;
    /*（默认值）：如果项目未设置高度或设为auto，将占满整个容器的高度*/
}

.align-items-baseline {
    align-items: baseline;
    /*项目的第一行文字的基线对齐*/
}

.align-items-center {
    align-items: center;
    /*垂直居中*/
}

.align-items-start {
    align-items: flex-start;
    /*顶部对齐*/
}

.align-items-end {
    align-items: flex-end;
    /*底部对齐*/
}