This div has width 50% but max-width 300px, so it will be whichever is the less of those two lengths.

This div has width 300px but min-width 50%, so it will be 300px wide unless that is less than 50% of the window, in which case it will be 50% of the window width.

The picture below has width 50% but max-width 300px, so it will be whichever is the less of those two lengths.

The picture below has width 300px but min-width 50%, so it will be 300px wide unless that is less than 50% of the parent div, in which case it will be 50% of the div width.