body {
    display: flex;
    flex-wrap: wrap;
    flex-direction: column;
    align-content: center;
    align-items: center;
    justify-content: center;
}

/*pc*/
@media screen and (min-width: 800px){
    body{
        padding: /*t*/3% /*r*/20% /*b*/0 /*l*/20%;
    }
    main{
        display: flex;
        flex-wrap: nowrap;
        justify-content: center;
        flex-direction: row;
    }
    #hello-text{
        display: flex;
        align-items: center;
        flex-direction: column;
        flex-wrap: nowrap;
    }
    #person-mobile{display: none;}
    #person-pc{display: block;}
}

/*mobile*/
@media screen and (max-width: 800px){
    body{    
        padding: /*t*/1% /*r*/5% /*b*/0 /*l*/5%;
    }
    main{
        display: flex;
        flex-wrap: wrap;
        flex-direction: column;
    }
    #hello-text{
        display: flex;
        align-items: flex-start;
        flex-direction: column;
        flex-wrap: nowrap;
    }
    #person-pc{display: none;}
    #person-mobile{display: block;}
}