Mega Nav

  <nav class="mega-nav">
    <ul class="nav nav--vertical nav--horizontal@lg nav--accordion nav--dropdown@lg position-relative" data-module="Nav">
      <li class="nav__item is-accordion-nav-parent is-dropdown-nav-parent position-static">
        <a class="nav__link is-active" href="...">...</a>
        <button class="button is-accordion-button">
          <span class="icon icon--chevron-down">
            [icon]
          </span>
        </button>
        <div class="is-accordion-nav is-dropdown-nav">
          <div class="flex-grid size-width-100">
            <div class="flex-grid__cell flex-grid__cell--span-6@sm">
              <ul class="nav nav--vertical">
                <li class="nav__item">
                  <a href="..." class="nav__link">...</a>
                </li>
                <li class="nav__item">
                  <a href="..." class="nav__link">...</a>
                  <ul class="nav nav--nested">
                    <li class="nav__item">
                      <a class="nav__link is-active" href="...">...</a>
                    </li>
                    ...
                  </ul>
                </li>
                <li class="nav__item">
                  <a href="..." class="nav__link">...</a>
                </li>
                ...
              </ul>
            </div>
            <div class="flex-grid__cell flex-grid__cell--span-6@sm">
              <ul class="nav nav--vertical">
                <li class="nav__item">
                  <a href="..." class="nav__link">...</a>
                </li>
                ...
              </ul>
            </div>
          </div>
        </div>
      </li>
      <li class="nav__item">
        <a class="nav__link" href="...">...</a>
      </li>
      ...
    </ul>
  </nav>