以 flex-direction: row 为参考。
以 justify-content: space-around 为参考。

flex-start 侧轴的起点对齐 （这里我们手动设置下子 view 的高度，来看的明显一些）。

假如 子view 没有单独设置高度的话，实际上效果和stretch一致。

1.Web

.contain {
    display: flex;
    flex-direction: row;
    justify-content: space-around;
    align-items: flex-start;
    width: 100vw;
    background:#ffff00;
}
.item {
    width: 100px;
}
.item1 {
    background-color: red;
    height: 50px;
}
.item2 {
    background-color: green;
    height: 70px;
}
.item3 {
    background-color: blue;
    height: 100px;
}

2.React Native

const styles = StyleSheet.create({
    container: {
        backgroundColor: '#ffffff',
    },
    contain: {
        display: 'flex',
        flexDirection: 'row',
        justifyContent: 'space-around',
        alignItems: 'flex-start',
        backgroundColor: '#fff000',
    },
    item: {
        width:100,
    },
    item1: {
        backgroundColor:'#da3800',height:50
    },
    item2: {
        backgroundColor:'#447e00',height:70
    },
    item3: {
        backgroundColor:'#0500ff',height:100
    },
});

3.微信小程序

.contain{
  display: flex;
  flex-direction: row;
  justify-content: space-around;
  align-items: flex-start;
  background-color: yellow;
  width: 100%;
}
.item {
  width: 100px;
}
.item1 {
  background-color: red;
  height: 50px;
}
.item2 {
  background-color: green;
  height: 70px;
}
.item3 {
  background-color: blue;
  height: 100px;
}