Hey hungrywatching,
I like to use this article for reference:
https://css-tricks.com/NetMag/FluidWidthVideo/Article-FluidWidthVideo.php
Looks like this section is what will work for you but there are other options if it does not:
https://screencast.com/t/Mdyf36eXYQ
When I make the width of the video 100% in the inspector and hight auto it works:
https://screencast.com/t/HoA0o96X
So here are the steps I would take:
1. Try changing your iframe video width and hight like this:
<iframe src="https://www.youtube.com/embed/L6vBnnryIug" width="100%" height="auto" frameborder="0" allowfullscreen="allowfullscreen"></iframe>
2. If that does not work check and see if your theme has a custom css section where you can drop in the css code. If not then download a plugin that allows you to do this. There are tons out there but search “Simple Custom CSS” in your plugin section and that should work for you.
Drop the below code in.
video {
width: 100% !important;
height: auto !important;
}
3. If 1 and 2 don’t work let me know and we will go from there.