fix: remove white space and balance layout with invisible spacer

- Replace text spacer with truly invisible point mark
- Disable axes on spacer with axis=None
- Top row (set bars + spacer) now matches bottom row width
- Maintains horizontal alignment while balancing visual layout

Author: edmundmiller

altair_upset/upset.py

@@ -642,22 +642,18 @@ def UpSetVertical(
         .properties(width=cardinality_bar_width, height=matrix_height)
     )
 
-    # Create empty spacer for top-right area
+    # Create invisible spacer for top-right to balance layout
     spacer = (
-        alt.Chart(pd.DataFrame({"x": [0]}))
-        .mark_text()
-        .encode(text=alt.value(""))
+        alt.Chart(pd.DataFrame({"x": [0], "y": [0]}))
+        .mark_point(opacity=0, size=0)
+        .encode(x=alt.X("x:Q", axis=None), y=alt.Y("y:Q", axis=None))
         .properties(width=cardinality_bar_width, height=set_bar_height)
     )
 
     # Combine components vertically with cardinality bars
     upsetaltair = (
         alt.vconcat(
-            alt.hconcat(
-                set_bar_chart,
-                spacer,
-                spacing=0,
-            ).resolve_scale(x="shared"),
+            alt.hconcat(set_bar_chart, spacer, spacing=0),
             alt.hconcat(
                 matrix_view,
                 cardinality_bar_chart,

tests/__snapshots__/test_advanced_features/test_upset_vertical_snapshot[vega_spec].json

@@ -89,13 +89,22 @@
       "hconcat": [
         {
           "encoding": {
-            "text": {
-              "value": ""
+            "x": {
+              "axis": null,
+              "field": "x",
+              "type": "quantitative"
+            },
+            "y": {
+              "axis": null,
+              "field": "y",
+              "type": "quantitative"
             }
           },
           "height": 240.0,
           "mark": {
-            "type": "text"
+            "opacity": 0,
+            "size": 0,
+            "type": "point"
           },
           "name": "view_3",
           "width": 120
@@ -561,11 +570,6 @@
           "width": 680
         }
       ],
-      "resolve": {
-        "scale": {
-          "x": "shared"
-        }
-      },
       "spacing": 0
     },
     {