body {
    box-sizing: border-box;
    height: 100vh;
    display: flex;
    flex-direction: column;
    margin: 0;
    padding: 2px;
    background-color: gray;
}

h1, h2, h3, h4 {
    line-height: 0;
}

.top, .bottom {
    display: flex;
    box-sizing: border-box;
    border: 2px solid black;
    background-color: skyblue;
    border-radius: 10px;
    padding: 10px;
    flex: 0 0 65px;
}

.top {
    flex-direction: row;
    justify-content: space-between;
}

.container{
    box-sizing: border-box;
    height: 100%;
    border-radius: 10px;
    display: flex;
    flex-direction: row;
    flex: 1 1 640;
}

.left, .right {
    box-sizing: border-box;
    border: 2px solid black;
    border-radius: 10px;
    padding: 10px;
    background-color: plum;
    flex: 0 0 200px;

}

.main {
    box-sizing: border-box;
    border: 2px solid black;
    border-radius: 10px;
    padding: 10px;
    background-color: rgb(247, 247, 247);
    flex: 2 1 240px;
}

@media screen and (max-width: 640px) {
    body {
        flex-direction: column;
    }
    .container {
        height: auto;
        flex-direction: column;
    }
    .main {
        order: -1;
    }
    .left, .right {
        flex: 1 1 auto;
    }
}