JSFiddle - React, Tailwind, and code Playground

HTML

<body class='section'>
    <div class="outercontainer">
        <div class="containerrow1">
            <div class="topbar">Blah</div>
        </div>
        <div class="containerrow2">
            <main class="section-content">content section
                <br/>content section
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                <br/>content section content section
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                <br/>content section content section
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                <br/>content section content section
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                <br/>content section content section
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             ...

CSS

*, *:before, *:after {
    box-sizing: inherit;
}
html, body {
    height: 100%;
    margin: 0;
}
.topbar {
    display: flex;
    width: 100%;
    align-items: center;
}
.containerrow1 {
    margin: 15px;
    padding: 15px;
    display: flex;
    flex: 1;
    background-color: yellow;
}
.containerrow2 {
    margin: 15px;
    padding: 15px;
    display: flex;
    flex: 2;
    background-color: pink;
    height: 100vh;
    min-height: 0; /* new; resolves Firefox bug */
    min-width: 0; /* new; resolves Firefox bug */
}
.outercontainer {
    display: flex;
    flex-direction: column;
    background-color: black;
    height: 100%; /* new */
}
.section {
    display: flex;
    flex-direction: column;
    background-color: aliceblue;
    height: 100vh;
}
.section-nav {
    order: -1;
    background-color: blue;
}
.section-nav, .section-content, .section-ads {
    overflow-y: scroll;
    padding: 2em;
}

.section-ads { flex: 1; }