How to embed a YouTube video in Service Cloud Web Campaign page and optimizing it for mobile?

Content

I am able to embed a YouTube video within Service Cloud Marketing pages. However, I am trying to set the video so that it resizes to the maximum with of the screen accessing it. As of now, it takes up half the screen in a mobile browser. The code that I found below instructs me on how to do it but it doesn't seem to be working for me. Has anyone done this and have the code and instructions they can share? Is the marketing style sheet still ma.css and accessed through the file manager?

Code Snippet

             1. The code instructs you to add the following to the css style sheet (which I believe is ma.css found in Site Configuration/File Manager css directory from the console. Can anyone validate that all i need to do is open and change this file?)

.video-container {
	position:relative;
	padding-bottom:56.25%;
	padding-top:30px;
	height:0;
	overflow:hidden;
}

.video-container iframe, .video-container object, .video-container embed {
	position:absolute;
	top:0;
	left:0;
	width:100%;
	height:100%;
}

2. It then has you add the div tag on your document web page around the youtube embed line below.

<div class="video-container"><iframe.......></iframe></div>