[jinct]

To learn just enough CSS for your MVP:

Understand the box model

Understand flex box basics

Understand padding and margin

Experiment with laying out simple elements on a single HTML file (where you can iterate more quickly), then when you have what you want, make those same changes in your React app

If you spend one hour on each of these, you may be surprised by how capable you’ve become. The rest, as others have said, you will pick up naturally as you work on your project.

[toastal]

Depending on browser support, there's a good likelihood just skipping a lot of these things for CSS grid could be a shortcut. As a bonus, gap for gutters is widely supported and takes away a lot of the headaches of float and flex-based grid systems.