How to make textarea fill the width of its parent width?

<textarea style="width:100%">* will work in most cases.

If it doesn't, please provide more information!

_{* Note: for some reason, it will need the cols and rows attributes to validate. But setting a width or a height will override them, so put any value you want.}

I advise flex over width: 100%, as 100% often does not account for borders, causing horizontal scrolls to appear.

<div style="display: flex">
    <textarea style="flex: 1"></textarea>
</div>