HTML

<aside id="sidenav-open">
  <nav>
    <h4>My</h4>
    <a href="#">Dashboard</a>
    <a href="#">Profile</a>
    <a href="#">Preferences</a>
    <a href="#">Archive</a>

    <h4>Settings</h4>
    <a href="#">Accessibility</a>
    <a href="#">Theme</a>
    <a href="#">Admin</a>
  </nav>
  
  <!-- TODO: Devsite - Removed inline handlers -->
  <!-- <a href="#" id="sidenav-close" title="Close Menu" aria-label="Close Menu" onchange="history.go(-1)"></a> -->
</aside>

<main>
  <header>
    <a href="#sidenav-open" id="sidenav-button" class="hamburger" title="Open Menu" aria-label="Open Menu">
      <svg viewBox="0 0 50 40" role="presentation" focusable="false" aria-label="trigram for heaven symbol">
        <line x1="0" x2="100%" y1="10%" y2="10%" />
        <line x1="0" x2="100%" y1="50%" y2="50%" />
        <line x1="0" x2="100%" y1="90%" y2="90%" />
      </svg>
    </a>
    <h1>Site Title</h1>
  </header>

  <article>
    <h2>Totam Header</h2>
    <p>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Cum consectetur, necessitatibus velit officia ut impedit veritatis temporibus soluta? Totam odit cupiditate facilis nisi sunt hic necessitatibus voluptatem nihil doloribus! Enim.</p>
    <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Fugit rerum, amet odio explicabo voluptas eos cum libero, ex esse quasi optio incidunt soluta eligendi labore error corrupti! Dolore, cupiditate porro.</p>

    <h3>Subhead Totam Odit</h3>
    <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Fugit rerum, amet odio explicabo voluptas eos cum libero, ex esse quasi optio incidunt soluta eligendi labore error corrupti! Dolore, cupiditate porro.</p>
    <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Fugit rerum, amet odio explicabo voluptas eos cum libero, ex esse quasi optio incidunt soluta eligendi labore error corrupti! Dolore, cupiditate porro.</p>
    
    <h3>Subhead</h3>
    <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Fugit rerum, amet odio explicabo voluptas eos cum libero, ex esse quasi optio incidunt soluta eligendi labore error corrupti! Dolore, cupiditate porro.</p>
    <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Fugit rerum, amet odio explicabo voluptas eos cum libero, ex esse quasi optio incidunt soluta eligendi labore error corrupti! Dolore, cupiditate porro.</p>
  </article>
</main>

CSS


        body {
  display: grid;
  grid: [stack] 1fr / min-content [stack] 1fr;

  @media (max-width: 540px) {
    & > :matches(aside, main) {
      grid-area: stack;
    }
  }
}

#sidenav-open {
  --easeOutExpo: cubic-bezier(0.16, 1, 0.3, 1);
  --duration: .6s;

  display: grid;
  grid-template-columns: [nav] 2fr [escape] 1fr;

  @media (max-width: 540px) {
    position: sticky;
    top: 0;
    max-height: 100vh;
    overflow: hidden auto;
    overscroll-behavior: contain;

    visibility: hidden; /* not keyboard accessible when closed */
    transform: translateX(-110vw);
    will-change: transform;
    transition: 
      transform var(--duration) var(--easeOutExpo),
      visibility 0s linear var(--duration);
    
    &:target {
      visibility: visible;
      transform: translateX(0);
      transition: transform var(--duration) var(--easeOutExpo);
    }
  }

  @media (prefers-reduced-motion: reduce) {
    --duration: 1ms;
  }
}

#sidenav-button,
#sidenav-close {
  -webkit-tap-highlight-color: transparent;
  -webkit-touch-callout: none;
  user-select: none;
  touch-action: manipulation;

  @media (min-width: 540px) {
    display: none;
  }
}

JS


        const sidenav = document.querySelector('#sidenav-open')
const closenav = document.querySelector('#sidenav-close')
const opennav = document.querySelector('#sidenav-button')

// set focus to our open/close buttons after animation
sidenav.addEventListener('transitionend', e => {
  if (e.propertyName !== 'transform')
    return

  const isOpen = document.location.hash === '#sidenav-open'

  isOpen
    ? closenav.focus()
    : opennav.focus()

  if (!isOpen) {
    history.replaceState(history.state, '')
  }
})

// close our menu when esc is pressed
sidenav.addEventListener('keyup', e => {
  if (e.code === 'Escape')
    window.history.length
      ? window.history.back()
      : document.location.hash = ''
})