[Client] Loot "Cards" are invisible until hovered over by cursor.
In the Loot tab in the client, The cards are invisible if you scroll down. They are revealed as you move your cursor over the cards. This occurs every time the loot page is opened.
Next, hovering the cursor over Azir, the top right squares are revealed, then moving the cursor down--parts of the bottom four are revealed.
Edit: Also occurs if you scroll down and back up, or vice versa. Anything not currently on your screen is blacked out until a cursor is moved over it.
