invalid tag case

src/textual/content.py

@@ -19,6 +19,7 @@
 from rich._wrap import divide_line
 from rich.cells import set_cell_size
 from rich.console import OverflowMethod
+from rich.errors import MissingStyle
 from rich.segment import Segment, Segments
 from rich.terminal_theme import TerminalTheme
 from rich.text import Text
@@ -744,9 +745,12 @@ def render(
 
             @lru_cache(maxsize=1024)
             def get_style(style: str, /) -> Style:
-                visual_style = Style.from_rich_style(
-                    app.console.get_style(style), app.ansi_theme
-                )
+                try:
+                    visual_style = Style.from_rich_style(
+                        app.console.get_style(style), app.ansi_theme
+                    )
+                except MissingStyle:
+                    visual_style = Style()
                 return visual_style
 
         else:

tests/snapshot_tests/test_snapshots.py

@@ -3316,12 +3316,16 @@ def compose(self) -> ComposeResult:
 def test_static_markup(snap_compare):
     """Check that markup may be disabled.
 
-    You should see two labels, the first uses markup.
-    The second has markup disabled, and tags should be visible.
+    You should see 3 labels.
+
+    This first label contains an invalid style, and should have tags removed.
+    The second label should have the word "markup" boldened.
+    The third label has markup disabled, and should show tags without styles.
     """
 
     class LabelApp(App):
         def compose(self) -> ComposeResult:
+            yield Label("There should be no [foo]tags or style[/foo]")
             yield Label("This allows [bold]markup[/bold]")
             yield Label("This does not allow [bold]markup[/bold]", markup=False)