Adds fallback support for the HTML5 <a href="http://html5doctor.com/the-details-and-summary-elements/" rel="nofollow ugc"><details> and <summary> elements</a> in browsers that don’t support them using <a href="http://mathiasbynens.be/notes/html5-details-jquery" rel="nofollow ugc">Mathias Bynens’ <details>/<summary> jQuery plugin.</a>
Once the plugin is activated on your site, the following HTML should work in all modern browsers, even if they don’t natively support the <details> and <summary> elements:
<pre><code><details>
 <summary>Click for more info...</summary>
 This is where you'd add the additional content that won't be seen until the "summary" is clicked.
</details>
</code></pre>

HTML5 Details Polyfill

Adds fallback support for the HTML5 <details> and <summary> elements in browsers that don't support them.

Designer023

IE 7 and 8 don’t do CSS3 or Media queries so instead of adding the fixes to your theme you can add them via a plugin. This means when they finally die a death you can drop support without having to update your theme. This also covers purchased themes so you don’t need to alter the actual files.

Compatiblizr

Plugin for patching old versions of IE (7 and 8)to work with CSS3 selectors and Media Queries.

HTML5 Details Polyfill vs Compatiblizr