I have added some gifs to my page body, but the sizing is always huge, the gif expands from one edge of the browser to the other and I can’t see any way to resize it, even in the html. This looks bad on web since if you scroll down, there is a huge gif that is only required to be about 1/5th of the size. It’s worse on a mobile browser as it gets cut off and you only see the edge of the gif.  screen shot attached. 
How can I specify the size of the gif on the page?

Thanks