Video/gif embeds with Custom Media Support are really small

[Orrielel]

tl;dr of what I did

• Added minimum width to 400px
• Increased max height to 50% of viewport
• Changed the expand button to fit width ( 100% of viewport - 720 pixels based on UI elements )

Content width should still scale at 25% of viewport, but I'm not sure how the expand feature looks on higher resolutions than x1080.