Everything is flexible these days. If you write
grid-template-columns: 200px 200px 200px;, sure, you’d have equal-width columns, but that’s a rare day. What you usually mean is three columns of equal fluid width.
We’ve got fractional units for that, like
grid-template-columns: 1fr 1fr fr;. That’s usually fine, but they aren’t very sturdy like pixels. A large bit of media (or something like a
<pre>, or long bit of text like a URL) can cause those columns … Read article “Equal Width Columns in CSS Grid are Kinda Weird”