With one regular violet shard, the expected electricity damage bonus should be 30% if the additional electricity damage doesn't count itself, and 40% if it does. With two violet shards, the expected damage bonus should be 80% and 100% respectively. However, the damage bonus only comes out to 60% as seen below.
The Dex Sybaris, as pictured below, has a base damage of 75.1, rounded down to 75 ingame. 45 is 60% of 75, which means that the additional electricity damage is nowhere to be seen.