Which line of code allows the developer to control how much room elements will take on a webpage?

$.$flex$-$container $\{$

display: flex;

flex$-$direction: row;

font$-$size: $30$px;

text$-$align: center;

$\}$

html $\{$

box$-$sizing: border$-$box;

$\}$

$*\{$

box$-$sizing: border$-$box;

$\}$

media $($max$-$width: $800$px$)\{$

$.$flex$-$container $\{$

flex$-$direction: column;

$\}$