Your image is the shadow you want on the table, seen from above — black is light, white is dark. A sample also sets the pattern settings it was drawn for.
Rounds cutout corners. Even 0 leaves a slight chamfer. If fine detail is disappearing, raise the resolution — lowering this will not bring it back.
Openings at the base let air reach the candle — a starved tealight smokes and goes out. Set to 0 only for an LED tealight.
Open flame: print in PETG, or use an LED tealight. PLA starts softening around 60 °C.