better ghosts

slides/lib.typ

@@ -30,10 +30,18 @@ pirat-color.red,
   }
 ]
 
-#let ghost(img, ..args,) = {
-  move(
+#let ghost(img, dx: 0pt, dy: 0pt, height: 100pt, ..args,) = context {
+  let img = image(img, height: height)
+  let s = measure(img)
+  let hx = s.width / 2
+  let hy = s.height / 2
+
+  place(
+    bottom + left,
+    dx: dx - hx,
+    dy: -dy + hy,
     ..args,
-    image(img, height: 100pt)
+    img
   )
 }