Why does this work:
left: calc(50vw - (269 * (100vw / 1220 ) ) );
But this doesn't:
left: calc(50vw - (269 * (100vw / 1220 ) ) + 269 );
The only difference being + 269.
FF inspector says 'invalid property value'.
When using calc(), you can multiply and divide by unitless values, but addition or subtraction requires units.
calc(10vh * 2) — This is ok, and means "I want twice as many vh as I started with".
calc(10vh + 2) — This isn't ok. "Plus two what: vh? px?".