html, body{
    margin: 0;
    /* padding: 0; */
}
:root{
    --h_header : 5rem ;
}
body{
    padding-top: var(--h_header) ;
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: calc(100vh - var(--h_header));
}
header{
    /* position: fixed; */
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    min-height: var(--h_header) ;
}
main{
    flex-grow: 1;
}