Huh. In CSS a percentage would calculate based on the width of the parent, but it looks like Figma is actually resolving it as a percentage of the font size. That’s an interesting decision. It’s neither translatable to CSS / iOS / Android without conversion, nor does it hew to the traditional typographic standard. On the other hand, it’s perhaps more understandable as a relative unit to the font size.
(Edit: It looks like Figma’s CSS export does auto-convert from percentage to an em unit, which is helpful.)
Regardless, I’ll see what we can do about getting this in for you. Besides the unit decision, there’s some complexity around the hug calculation when letter spacing is in play, so it may be a few releases out.