What does a `~` tilde in a CSS `url()` do?

The CSS @import path <url> is usually relative to the current working directory.

So using the prefix ~ at the start of the path tells Webpack's css-loader to resolve the import "like a module", starting from the node_modules directory.

What that means is that if you have a node module called normalize installed, and you need to import a css file from within it named /normalize.css, you can do that with:

@import "~normalize/normalize.css";

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In your linked example, inside font-loader/example/test.js there is an import of a module called font-boon.

var boon = require('./font-boon');

Inside of font-loader/example/test.css the font-boon module is @imported so that it is available in text.css.

@import url("~./font-boon");

UPDATE March 2021

From sass-loader tilde '~' imports are deprecated and is recommended to be removed.