Oops, it doesn't look like 'monument on a dark day' is a national day..

Other days

youth

Youth Day
self appreciation

Self Appreciation Day
tulip

Tulip Day
boy friend

Boy Friend Day
boba

Boba Day
girl friend

Girl Friend Day
gum

Gum Day
mean girls

Mean Girls Day
ponytail

Ponytail Day
lisp

Lisp Day