https://cssgridgarden.com/

This is quite possibly the best tool for learning CSS grid I've used, personally. If you're struggling to learn the concepts of CSS Grid, or if you're a new dev and just starting CSS, this is a great tool.

This site creates a fun little crop farming game that teaches the core concepts of CSS grid by allowing you to plant carrots in each grid, depending on the code you write. You also have water/irrigation to take into consideration, so your carrots are perfectly taken care of. In my opinion, this is the best tool for CSS grid out there!