[css] SASS - use variables across multiple files

This question was asked a long time ago so I thought I'd post an updated answer.

You should now avoid using @import. Taken from the docs:

Sass will gradually phase it out over the next few years, and eventually remove it from the language entirely. Prefer the @use rule instead.

A full list of reasons can be found here

You should now use @use as shown below:

_variables.scss

$text-colour: #262626;

_otherFile.scss

@use 'variables'; // Path to _variables.scss Notice how we don't include the underscore or file extension

body {
  // namespace.$variable-name
  // namespace is just the last component of its URL without a file extension
  color: variables.$text-colour;
}

You can also create an alias for the namespace:

_otherFile.scss

@use 'variables' as v;

body {
  // alias.$variable-name
  color: v.$text-colour;
}

EDIT As pointed out by @und3rdg at the time of writing (November 2020) @use is currently only available for Dart Sass and not LibSass (now deprecated) or Ruby Sass. See https://sass-lang.com/documentation/at-rules/use for the latest compatibility