The lessons are correct, but may be more obvious with better definitions.
"Alive" pieces remain permanent throughout the game. In both 2.16 examples, white can capture black by filling the gaps.
"Eyes" only have one space each and are fully surrounded by a single color. In both 2.16 examples. there are no eyes. Look at 2.17 with this new definition to see where the gaps are not yet eyes.
2.17 (3) is asking you to place a white piece within the black formation. This renders correctly for me in firefox.
Here's a link to a screenshot of what I see so you can see what I'm talking about: https://imgur.com/a/odDYg9K
Ah, I see. Not rendering white makes these lessons impossible.
It's interesting that the shading for the white pieces is preserved. I wonder if a dark mode extension is affecting the colors.
oooo I'm dumb lol. Yea I'm forcing dark mode
I'm glad we figured it out! Have fun.