[pen2l]

Here is perhaps a controversial suggestion:

don't! Just use boostrap studio ( https://bootstrapstudio.io ) or something (there exist free alternatives if you don't like paying 25 bucks) :)

[seivan]

I think the friend in question is trying to get a job. At that point, knowing flexbox or using grid classes might not be enough for an interview. Naturally, I'm guessing on both accounts.