I know CSS and believe me it sucks. Sure grid layout and flexbox fix things. But a lot of it is hacks on top of hacks.
Why do you think the padding as a percentage is relative to the width of the parent? Do you think it was a happy accident? I don't think so, it was purposefully put there in the specs so that we could have boxes with fixed aspect ratios. This is just the tip of the iceberg.
The good thing is that all the hacks together make a working thing. And if you know them you can do a lot of stuff.
Why do you think the padding as a percentage is relative to the width of the parent? Do you think it was a happy accident? I don't think so, it was purposefully put there in the specs so that we could have boxes with fixed aspect ratios. This is just the tip of the iceberg.
The good thing is that all the hacks together make a working thing. And if you know them you can do a lot of stuff.