Simon Willison’s Weblog

The Cleanest Trick for Autogrowing Textareas (via) This is a very clever trick. Textarea content is mirrored into a data attribute using a JavaScript one-liner, then a visibility: hidden ::after element clones that content using content: attr(data-replicated-value). The hidden element exists in a CSS grid with the textarea which allows the textarea to resize within the grid when the hidden element increases its height.