Answer 1

Good question

https://developer.mozilla.org/en-US/docs/Web/CSS/flex#%3C'flex-grow'%3E

One-value syntax: the value must be one of:
a <number>: In this case it is interpreted as flex: <number> 1 0; the <flex-shrink> value is assumed to be 1 and the <flex-basis> value is assumed to be 0.

So,

Add flex-shrink: 1; and flex-basis: 0;

and you should see outcome same as flex: 1;

https://code.sololearn.com/Wko1dtuqMdbM/?ref=app