Add example to compare border and outline.

docs/examples/styles/outline_vs_border.css

@@ -0,0 +1,11 @@
+Label {
+    height: 8;
+}
+
+.outline {
+    outline: $error round;
+}
+
+.border {
+    border: $success heavy;
+}

docs/examples/styles/outline_vs_border.py

@@ -0,0 +1,21 @@
+from textual.app import App
+from textual.widgets import Label
+
+
+TEXT = """I must not fear.
+Fear is the mind-killer.
+Fear is the little-death that brings total obliteration.
+I will face my fear.
+I will permit it to pass over me and through me.
+And when it has gone past, I will turn the inner eye to see its path.
+Where the fear has gone there will be nothing. Only I will remain."""
+
+
+class OutlineBorderApp(App):
+    def compose(self):
+        yield Label(TEXT, classes="outline")
+        yield Label(TEXT, classes="border")
+        yield Label(TEXT, classes="outline border")
+
+
+app = OutlineBorderApp(css_path="outline_vs_border.css")