However, I must say, it's 2019, if you call yourself a front-end developer, and you do not know flexbox and grid - you are greatly missing out on an amazing radical change in how you think about and design your layouts. There really is no excuse for not knowing this stuff, especially with all the great resources out there to help you learn.
Flexbox Zombies basically changed my life. It taught me the possibilities, and now I know them by hand. https://mastery.games/p/flexbox-zombies
The same company has a paid game to learn about the grid (https://gridcritters.com/), but I came across the resources below and did not buy it.
Flexbox Froggy and Grid Garden are both free, not gated by an email signup, and very high quality. You and everyone on your team should do them, even if you think you know them well. It will help with reinforcement.
- https://flexboxfroggy.com/ - https://cssgridgarden.com/
I think Gimli is an amazing tool, and I might even buy it when it comes out. But please, do yourself and your team a favor - learn the tools by hand first. If you wrote a float at all this year, this post goes out to you.