#container {
    /* border: 1px solid rgb(32, 76, 221); */
}

div {
    /* border: 1px solid black; */
}

#container > *:not(#middle-flow), #middleflow >* {
    /* wybór wszystkich pierwszych elementów */
    
    min-height: 100px;
    
    display: flex;
    justify-content: center;
    align-items: center;
    
    }

    
#middle-flow {
    display: table; 
    width: 100%;   
}

#middle-flow > *{
    display: table-cell;
}


header {
    background-color: green;
}
nav {
    padding: 1.5em 0.3em;
    background-color: rgb(59, 59, 230);
}
 
article {

    background-color: yellow;

    width: 60%;

    padding: 1.5em 2em;
    /* margin: 0 10px; */
}
 
aside {
    padding: 1.5em 0.3em;
    background-color: teal;
}
 
footer {
    background-color: red;
}

@media print {
    * { 
        background: none;
        color: black;
    }

    nav, header, aside, footer {
        display: none !important;
    }
}