the min-height was in the way -- bugfix

Asset/css/shrink-vertically.css

@@ -18,7 +18,15 @@
  *
  * The selector is intentionally more specific than core's single-class rule, and
  * uses !important, so this override wins even alongside a theme (e.g. Essential).
+ *
+ * The min-height override is essential: Kanboard's drag-and-drop sets an INLINE
+ * min-height on each column equal to its full content height
+ * (BoardDragAndDrop.js: css("min-height", parent().height())). In CSS, min-height
+ * beats max-height, so that inline value keeps tall columns from shrinking and our
+ * max-height alone does nothing. A stylesheet !important overrides the inline
+ * (non-important) min-height, so we reset it to 0 and let max-height win.
  */
 #board td .board-task-list.board-task-list-compact {
     max-height: calc(100vh - 170px) !important;
+    min-height: 0 !important;
 }