Error importing switch extension

[PhilAnderson1]

I have the following lines in my project file, with bulma-switch.sass added to the bulma directory as per the instructions:

@import "bulma-0.7.4/bulma.sass";
@import "bulma-0.7.4/sass/extensions/bulma-switch.sass";

And I'm getting the following error:

sass --sourcemap=none sp.scss:sp.css
Error: Incompatible units: 'rem' and 'px'.
on line 14 of bulma-0.7.4/sass/extensions/bulma-switch.sass, in `switch-size'
from line 148 of bulma-0.7.4/sass/extensions/bulma-switch.sass
from line 65 of sp.scss
Use --trace for backtrace.