The flex-basis property sets the flex-basis longhand, which specifies the flex basis: the initial main size of the flex item, before free space is distributed according to the flex factors.
object.style.flexBasis = "value";
<'flex-basis'> = content | <'width'>
Indicates an automatic size based on the flex item's content.
<'width'> = auto | <length-percentage> | min-content | max-content | fit-content( <length-percentage> )
Automatically specified by the user agent.
<length-percentage> = [ <length> | <percentage> ]
Specifies the length using a number followed by a unit of measurement.
Specifies the percentage using a number followed by a percent sign (%).
Represents the largest min-content contribution of the items occupying the track.
Represents the largest max-content contribution of the items occupying the track.
Represents the formula max(minimum, min(limit, max-content)), where minimum represents an auto minimum (which is often, but not always, equal to a min-content minimum), and limit is the track sizing function passed as an argument to fit-content(). This is essentially calculated as the smaller of minmax(auto, max-content) and minmax(auto, limit).
World Wide Web Consortium (W3C)