* {
    margin: 0;
    padding: 0;
}

body {
    display: flex;
    flex-wrap: wrap;
    flex-direction: row;
}

header {
    height: 20vh;
    flex: 1 1 100%;
    background-color: lightgreen;
}

#Hauptbereich {
    height: 70vh;
    display: flex;
    flex-direction: row;
    align-items: stretch;
}

nav {
    height: 70vh;
    flex: 1 1 15%;
    background-color: yellow;
}

main {
    height: 70vh;
    flex: 1 1 70%;
    text-align: center;
    background-color: rosybrown;
}

#MainTeile {
    height: 65vh;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: space-around;
    align-items: stretch;
}

section {
    width: 30%;
    min-width: 300px;
    margin: 5px;
    padding: 5px;
    border: black 2px solid;
    border-radius: 20px;
    background-color: white;
}

aside {
    height: 70vh;
    flex: 1 1 15%;
    background-color: lemonchiffon;
}

footer {
    height: 10vh;
    flex: 1 1 100%;
    background-color: red;
}