But it's not how long they've been around, it's whether they're built into standard browsers. Presumably, CSS variables can never be removed from standard brows

But it's not how long they've been around, it's whether they're built into standard browsers. Presumably, CSS variables can never be removed from standard browsers. They are permanently available in the web "toolchain". SASS can be replaced by something else. There will be workarounds, but it will probably be more of a problem.