Melt your preferred color of chocolate button/chips, pour into piping bag/ziplock and fill the cavities. You can also do this just with your spoon, carefully, so you won't make much of a mess. Chill in the fridge for 10 mins or until firm.
For the flowers, I cut an empty tissue roll (or you can use paper roll for wrapping or kitchen paper roll as well) as shown. Melt my chocolate, pour into ziplock and snip the corner, and pipe a dollop of melted chocolate each time. With the back of a spoon, I press it onto melted chocolate and pull the chocolate down, on a parchment paper that is cut close to or exact size to the tissue roll . Lift the parchment paper and place carefully inside the tissue roll. Chill in the fridge for 10 mins or until these petals are firm.
Line a parchment paper on a plate/cutting board, and pipe a dollop of chocolate. Start stacking petals and form into a flower. Each time you stack the petal, dab a little melted chocolate. Once your flower is formed, pipe a little melted chocolate in center and press a chocolate button. Chill for 10 mins/until firm in the fridge.
Same as for making "lazy person" leaves. Melt chocolate and pipe on parchment. Pull down melted chocolate with the back of a spoon and chill.
Cover the whole cake with buttercream, attach chocolate fence on the side of the cake, and decorate the top of the cake with chocolate flowers and leaves.