ADA compliance

[jaymollica]

Right now the alerts are nested in the <nav>, this is misleading to a screen reader. Only navigational items should be nested in <nav>. A good step forward would be to put it outside <nav> and make visible elements hidden from screen readers, then create a new element that is offscreen (ie -9999px to the left) that a screen reader would pick up on.

<div class="screen-reader-alert-container">
<h1>Tips for visiting SFMOMA today</h1>
<ul>
<li>Alert 1</li>
<li>Alert 2</li>
...
</ul>
</div>