Stacked Bar (Vega-Lite)

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "title": "Stacked Bar Chart",
  "width": 300,
  "height": 180,
  "data": {
    "values": [
      {"region": "A", "category": "X", "value": 28},
      {"region": "A", "category": "Y", "value": 55},
      {"region": "B", "category": "X", "value": 43},
      {"region": "B", "category": "Y", "value": 91},
      {"region": "C", "category": "X", "value": 81},
      {"region": "C", "category": "Y", "value": 53}
    ]
  },
  "mark": "bar",
  "encoding": {
    "x": {"field": "region", "type": "nominal", "title": "Region"},
    "y": {"field": "value", "type": "quantitative", "title": "Value"},
    "color": {"field": "category", "type": "nominal", "title": "Category"}
  }
}