#app {
    width: 100vw;
    height: 100vh;
    padding: 0px;
    margin: 0px;
    display: flex;
    flex-direction: column;
}

#header {
    flex-basis: 50px;
    border: 1px solid red;
    max-height: 50px;
}

#main {
    flex-grow: 1;
    border: 1px solid red;
}

#footer {
    flex-basis: 100px;
    max-height: 100px;
    border: 1px solid red;
}