[STYLE] Nav tabs - reduce top margin to 0.5rem
[STYLE] Nav tabs - reduce top margin to 0.5rem

To avoid wasting too much space at the top of the page

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods