Gridlines in ListView

try this mixin:

{
  "name": "Application",
  "appearances": {
    "listview/grid-row": {
      "states": {
        "default": {
          "styles": {
            "widthBottom": 1,
            "colorBottom": "windowFrame",
            "backgroundColor": "table-row-background"
          },
          "properties": {
            "textColor": "table-row"
          }
        },
        "selected": {
          "styles": {
            "backgroundColor": "table-row-background-selected"
          },
          "properties": {
            "textColor": "table-row-selected"
          }
        }
      }
    }
  }
}

It’s a theme property. I can send you a mixin.theme definition. Vertical, horizontal or both?