#mainvisual{
    display: block;
    aspect-ratio: auto;
    width: 100%;
    margin: 20px auto 0px; 
    overflow: auto;
}

#mainvisual img{
width: 100%;
height: auto;
}

#mainvisual img:first-child{
    margin-bottom: 20px;
}

@media screen and (min-width: 834px) {
    #mainvisual{
        display: flex;
        justify-content: space-between;

    }
    
    #mainvisual img{
    width: 48%;
    height: auto;
    }

    #mainvisual img:first-child{
        margin-bottom: 0px;
    }
}