On March 3, we'll be updating the embedded timeline to better showcase the stories you tell with Tweets. The new timeline features a clean, modern design which showcases expanded photos, videos, GIFs, and more. It's fully responsive and includes support for a number of new media types, including polls.
To see what your existing timelines will look like in the new design during the preview period, simply add
<meta name="twitter:widgets:new-embed-design" content="on"> to your page. And you can read more about the new embedded timeline design on the Twitter developer blog.