body{
    margin:0;
}
.page {
    margin:2em;
    background-color:#fff;
}
.page header, .page footer {
    background-color:#ccc;
    padding: 1.3em;
    font-weight:bold;
    color: black;
    font-size:1.2em;
}
.page main {
    display:flex;
    flex-wrap:wrap;
    line-height:1.5em;
}
.page article {
    flex-basis:100%;
}
.page {
    margin:0;
}

/*TABLETTE*/
@media screen and (min-width:780px) and (max-width:1200px) {
    .page article {
        flex-basis:50%;
    }
}

/*DESKTOP*/
@media screen and (min-width:1200px) {
    .page article {
        flex-basis:25%;
    }
    .page {
        margin:2em;
    }
}