League of Legends (LoL) Question: How to do .Webm properly

Add a custom "width" to the end of the webm tag and it won't be so massive e.g. putting it to 500px (essentially means it'll be 500 pixels big), if you want to center it you could choose to use a "center" tag around the chosen clip.

You can also choose to add 2 other variables to the code, one called "autoplay" (makes the clip play automatically without readers or yourself having to click on it) which is turned on with the code autoplay=on as well as "loop" (makes the clip play over and over again) which has the same variable loop=on to work. Here's a brief example of how it'd work, hope it helps: