Fix dropdowns on backpack items being transparent

The blend-mode property was being set on the whole thing, rather than the image only

src/components/backpack/backpack.css

@@ -71,5 +71,8 @@
 .backpack-item {
     min-width: 4rem;
     margin: 0 0.25rem;
+}
+
+.backpack-item img {
     mix-blend-mode: multiply; /* Make white transparent for thumnbnails */
 }