Allow browsers to determine video or slideshow dimensions based on the width of their containing block by creating an intrinsic ratio that will properly scale on any device.
Rules are directly apply to <iframe>, <embed> and <object> elements, optionally use of an explicit descendant class .embed-responsive-item when you want to match the styling for other attributes.
Pro-Tip! You don't need to include frameborder="0" in your <iframe>s as we override that for you.