MDN web docs describes fit-content as a function:
https://developer.mozilla.org/en-US/docs/Web/CSS/fit-content
https://developer.mozilla.org/en-US/docs/Web/CSS/width#fit-content
width: fit-content(20em);
I can't find any reference to fit-content being defined as a value without the parentheses as it is here:
figure {
width: fit-content;
}
What is the difference?
You need to refer to the specification to find them:
Value: auto | | min-content | max-content | fit-content(
<length-percentage>)
This is the Box Sizing Level 3 specification.
Later in the Level 4 you can read:
New values: stretch | fit-content | contain
And
fit-content
Essentially fit-content(stretch) i.e. min(max-content, max(min-content, stretch)).
So fit-content = fit-content(stretch)
stretch
Applies stretch-fit sizing, attempting to match the size of the box’s margin box to the size of its containing block. See § 7.1 Stretch-fit Sizing: filling the containing block.