drop-shadow() reuses box-shadow's own concentric-fill blur approximation, keyed off the filtered element's own border-box rectangle rather than a true per-pixel alpha silhouette of its content. (docs/html-css-support.md#filters-and-blend-modes)
offset only, no blur filter: drop-shadow(10px 10px 0 rgba(0,0,0,0.45)) | offset + blur filter: drop-shadow(6px 6px 8px rgba(0,0,0,0.5)) | colored shadow filter: drop-shadow(-8px 8px 10px rgba(41,128,185,0.6)) |