Because I plan to put the button in the red box in the picture below at the end of this row
But when I give the div in the button a width of 100%, the following picture will appear, that is, the position will be messed up
Later, change width:100%; to flex-grow: 1; the effect is as follows
flex-grow:
For details, please refer to flex-grow - CSS: Cascading Style Sheets | MDN (mozilla.org)