<style>
main {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
}
header {
    position: -webkit-sticky;
    top: 0;
    z-index: 1;
    padding: 40px;
    border-top: 1px solid blue;
    border-right: 1px solid green;
    border-bottom: 1px solid black;
    border-left: 1px solid red;
    background-color: lightgrey;
}
section {
    position: relative;
    padding: 80px;
}
</style>

<main>
    <div class="wrapper">
        <header>Level 1 Header</header>
        <section>
            Level 1 Content
            <div class="wrapper">
                <header>Level 2 Header</header>
                <section>
                    Level 2 Content
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                </section>
                <header>Level 2 Header</header>
                <section>
                    Level 2 Content
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                </section>
            </div>
            <div class="wrapper">
                <header>Level 2 Header</header>
                <section>
                    Level 2 Content
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                </section>
                <header>Level 2 Header</header>
                <section>
                    Level 2 Content
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                    <div class="wrapper">
                        <header>Level 3 Header</header>
                        <section>Level 3 Content</section>
                    </div>
                </section>
            </div>
        </section>
    </div>
</main>