[css] Add the management of a "blank" value for our borders

sandbox/borders.py

@@ -0,0 +1,65 @@
+from rich.console import RenderableType
+from rich.text import Text
+
+from textual.app import App, ComposeResult
+from textual.css.types import EdgeType
+from textual.widget import Widget
+from textual.widgets import Placeholder
+
+
+class VerticalContainer(Widget):
+    CSS = """
+    VerticalContainer {
+        layout: vertical;
+        overflow: hidden auto;
+        background: darkblue;
+    }
+
+    VerticalContainer Placeholder {
+        margin: 1 0;
+        height: 5;
+        align: center top;
+    }
+    """
+
+
+class Introduction(Widget):
+    CSS = """
+    Introduction {
+        background: indigo;
+        color: white;
+        height: 3;
+        padding: 1 0;
+    }
+    """
+
+    def render(self, styles) -> RenderableType:
+        return Text("Here are the color edge types we support.", justify="center")
+
+
+class MyTestApp(App):
+    def compose(self) -> ComposeResult:
+        placeholders = []
+        for border_edge_type in EdgeType.__args__:
+            border_placeholder = Placeholder(
+                id=f"placeholder_{border_edge_type}",
+                title=(border_edge_type or " ").upper(),
+                name=f"border: {border_edge_type} white",
+            )
+            border_placeholder.styles.border = (border_edge_type, "white")
+            placeholders.append(border_placeholder)
+
+        yield VerticalContainer(Introduction(), *placeholders, id="root")
+
+    def on_mount(self):
+        self.bind("q", "quit")
+        self.bind("t", "tree")
+
+    def action_tree(self):
+        self.log(self.tree)
+
+
+app = MyTestApp()
+
+if __name__ == "__main__":
+    app.run()