Think of auto as letting the browser make the sizing decision instead of supplying a fixed measurement. In Flexbox, it appears as an allowed value for flex-basis, the starting size of a flex item. section 12.6
When you meet auto in a Flexbox rule:
- Read it as “let the browser calculate this part.” section 12.6
- Remember that surrounding Flexbox behavior can still grow or shrink items to fit the container. section 12.6
A flexible starting point
Use `flex-basis: auto` when the item's starting size should be handled automatically rather than fixed with a value such as `10em`. The shorthand `flex: 0 1 auto` combines that basis with Flexbox growth and shrinking settings. section 12.6
item {
flex-basis: value|auto|content;
}
Compare auto with other permitted flex-basis values in the compact declaration pattern. section 12.6
