Why doesn't it work?(css)

Question

I found a cheat sheet but it's not working.
What should I do?
https://code.sololearn.com/Ws336CjCgqaK/?ref=app

Answer 1

Don't write everything in your css file inside your body.
Don't write:
body {
.button {
...
}
...
}
Write instead:
body {
}
.button {
...
}
...

Answer 2

Thanks