header {
    width: 100%;
    height: 10vh;
    text-align: center;
    background-image: url('lebka.jpg');
    display: block;
    COLOR: white;
    border: 2px solid red;
}

footer {
    clear: both;
    width: 100%;
    background-color: gray;
    border: 2px solid red;
    text-align: center;
}

img {
    max-height: 60vh;
}

.row {
    display: flex;
}

nav {
    flex: 1;
    padding: 1em;
    border: 2px solid red;
    background-color: yellowgreen;
}
article {
    flex: 5;
    padding: 1em;
    border: 2px solid red;
    /*background-color: lightblue;*/
}

table {
    border-collapse: collapse;
}
table, tr, td, th {
    border: 3px ridge whitesmoke;
}

#nonffwarning {
    color: red;
    text-align: center;
    font-size: 1em;
}