I agree, but I would extend it a bit: For a junior the answer is more "I'll just use bootstrap and customize as much as needed". While for a senior it's more

I agree, but I would extend it a bit: For a junior the answer is more "I'll just use bootstrap and customize as much as needed". While for a senior it's more in line with "I'll just use bootstrap, but you bet I will be on the designer's ass if they ask to customize stuff where it's not necessary." There is a reason the mid-level developer wanted to write custom CSS. And the reason is that they didn't have the political capital to make bootstrap alone work in a way that is good for the company.