YouTube embedded videos display too large

When I embed YouTube videos on my pages, they display across the entire width of the page. I have made sure to reduce the size in the embed code of the video, however this does not help.

For example, a video sized at 300px x 225px fills the entire screen.

<iframe width=”300″ height=”225″ src=”//www.youtube.com/embed/5xdpDjodGoU” frameborder=”0″ allowfullscreen></iframe>