CSS - Overflow

Visually-hidden styles are used to hide content from most users, while keeping it accessible to assistive technology users.

It works because the content is technically visible and displayed — it appears in the accessibility tree and the render tree, both of which are used by assistive technologies — it’s just that the rendered size is zero.

Our industry has largely settled on a standard CSS pattern for this, refined over years of testing and iteration, by many people. This pattern:

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This article is not about when or why you would use visually-hidden content. There’s a number of excellent articles that discuss these questions in detail, notably Scott O’Hara’s Inclusively Hidden. But most of them don’t go into much detail about the specific CSS involved — why do we use this particular pattern, with these specific properties? So today I’m going to dissect it, looking at each of the properties in turn, why it’s there, and why it isn’t something else.

[T]he problem highlighted by the CSS is Awesome meme […] is an issue of overflow. You have made a fixed width container and are trying to put content into that container which is too big, what do you want CSS to do here?

CSS by default will do what you see in the meme because to do anything else would cause data loss, which [in] CSS terms means that some of your content vanishes.

We try and avoid data loss because if something on your page vanishes at certain screen sizes – because of overlap, or it going off the side of the screen, you may be unaware of it. A quick eyeballing of the page may not cause something missing to jump out at you. You will tend to spot the messy overflow though.

A good example of this design pattern can be seen in the Box Alignment specification, with the safe and unsafe alignment keywords. Safe alignment, means that your chosen alignment method won’t be used if it causes data loss, unsafe means that data loss may happen.

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Better ways to stop content just “honking out of the box”

The author of the meme wondered why the box didn’t grow to fit the content. However if you give something a fixed size in CSS, it will respect that size. What the author really wanted was to make the box min-content sized. With a box that has a width of min-content the box will grow as big as it needs to be to contain the content, with all soft-wrapping opportunities taken, but no bigger.

If instead, you want to make the box not wrap at all, then give it a width of max-content. The text will then display all as one line and take no soft-wrapping opportunities.

Perhaps you need to have the box that fixed width, but don’t mind if it grows taller. In that case use overflow-wrap: break-word.

Take a look at [this CodePen] for all your awesome possibilities.