The code that follows

padding: $\mathrm{.}5$em $0.25$em;

applies this padding to an element:

$\mathrm{.}5$em above, $0$ left, and $\mathrm{.}25$ em below

$\mathrm{.}5$ em above, $0$ left and right, and $\mathrm{.}25$ em below

$\mathrm{.}5$ em above and below, $0$ right, and $\mathrm{.}25$ em left

$\mathrm{.}5$ em above, $0$ right, and $\mathrm{.}25$ em below