*{
    box-sizing: border-box;
}

nav{
    padding: 10px;
}

header{
    padding: 10px;
}

body{
    margin: 0;
}

main{
    width: 50%;
    float: left;
    padding: 10px;
}

.gallery{
    display: inline-block;
    max-width: 600px;
}

.gallery img{
    width: 100%;
    height: auto;
}

@media screen and (max-width:600px){
    main, body{
        width: 100%
        }
    }