Embedded Twitch style doesn't work

API
2

You set the width and height in percentages
So the iframe will grow to the size of the parent div.
so the parent div which is .content doesn’t have a lot of height to play with.
So you get unexpected dimensions.

So you can see the the iframe is 80% of the widgth of the parent
And 100% of the height of the parent.

The parent doesn’t have any height as 100% of nothing is nothing. (the parent is not 100% height of the web page as “natural” websites don’t have a defined height)
But the parent did is display block so has the width of the webpage.

So your code is correct, but the parent div has no height

This isn’t a fault in the embed but your website css.

A common fix/hack is to make the parent did have height.
Or if it’s supposed to be 100% of the page, set the parent div to (which is a cheat but a start point to get you going)

.content {
    position: absolute;
    top: 0px;
    left: 0px;
    right: 0px;
    bottom: 0px;
}