JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div class="menu">
        1
    </div>
    <div class="content">
        <div class="wrapper-inner">
            2
            <div class="half">
                2.1
            </div>
        </div>
    </div>
    <div class="footer">
        3
    </div>
</div>

CSS

body {
    margin: 0;
}

.wrapper {
    display: flex;
    flex-direction: column;
    height: 100vh;
}

.wrapper-inner {
    position: absolute;
    display: flex;
    flex-direction: column;
    height: 100%;
    width: 100%;
}

.content {
    background: green;
    flex: 1;
    position: relative;
}

.half {
    background: yellow;
    flex: 0 0 50%;
}

.menu {
    background: purple;
    flex: 0 0 70px;
}

.footer {
    background: cyan;
    flex: 0 0 100px;
}