Adam Argyle has a post over on web.dev digging into this. He starts with the assumption that you need to do vertical centering and horizontal centering. It’s that vertical centering that has traditionally been a bit trickier for folks, particularly when the height of the content is unknown.
Adam details five(!) methods for handling it, even getting into centering unknown vertical and horizontal dimensions, plus a handful of other restraints like language direction and multiple elements. I guess all the silly jokes about the difficulty of centering things in CSS need to be updated. Maybe they should poke fun about how many great ways there are to center things in CSS.
Adam does a great job listing out the pros and cons of all the techniques, and demonstrating them clearly. There is also a video. He picks “the gentle flex” as the winning approach:
You can always find it in my stylesheets because it’s useful for both macro and micro layouts. It’s an all-around reliable solution with results that match my expectations. Also, because I’m an intrinsic sizing junkie, I tend to graduate into this solution. True, it’s a lot to type out, but the benefits it provides outweighs the extra code.
Remember that when you’re “centering in CSS” it’s not always within these extreme situations. Let’s look at another situation, just for fun. Say you need to horizontally center some inline-*¹ elements… text-align: center; gets you there as a one-liner:
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But what if you need to center the parent of those items? You’d think you could do a classic margin: 0 auto; thing, and you can, but it’s likely the parent is block-level and thus either full-width or has a fixed width. Say instead you want it to be as wide as the content it contains. You could make the parent inline-*, but then you need another parent in which to set the text-align on to get it centered.
Stefan Judis talked about this recently. The trick is to leave the element block-level, but use width: fit-content;
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The ol’ gentle flex could have probably gotten involved here too, but we’d need an additional parent again. Always something to think about.
What I mean by inline-* is: inline, inline-block, inline-flex, inline-grid, or inline-table. Did I miss any?
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