[css] Use a HelpText for unknown CSS property name errors

tests/css/test_stylesheet.py

@@ -1,7 +1,10 @@
 from contextlib import nullcontext as does_not_raise
+from typing import Any
+
 import pytest
 
 from textual.color import Color
+from textual.css._help_renderables import HelpText
 from textual.css.stylesheet import Stylesheet, StylesheetParseError
 from textual.css.tokenizer import TokenizeError
 
@@ -60,6 +63,7 @@ def test_color_property_parsing(css_value, expectation, expected_color):
     [
         ["backgroundu", "background"],
         ["bckgroundu", "background"],
+        ["ofset-x", "offset-x"],
         ["colr", "color"],
         ["colour", "color"],
         ["wdth", "width"],
@@ -81,12 +85,17 @@ def test_did_you_mean_for_css_property_names(
         "${PROPERTY}", css_property_name
     )
 
+    stylesheet.add_source(css)
     with pytest.raises(StylesheetParseError) as err:
-        stylesheet.parse(css)
+        stylesheet.parse()
 
-    error_token, error_message = err.value.errors.stylesheet.rules[0].errors[0]
-    if expected_property_name_suggestion is None:
-        assert "did you mean" not in error_message
-    else:
-        expected_did_you_mean_error_message = f"unknown declaration '{css_property_name}'; did you mean '{expected_property_name_suggestion}'?"
-        assert expected_did_you_mean_error_message == error_message
+    _, help_text = err.value.errors.rules[0].errors[0]  # type: Any, HelpText
+    assert help_text.summary == f"Invalid CSS property [i]{css_property_name}[/]"
+
+    expected_bullets_length = 1 if expected_property_name_suggestion else 0
+    assert len(help_text.bullets) == expected_bullets_length
+    if expected_property_name_suggestion is not None:
+        expected_suggestion_message = (
+            f"Did you mean [i]{expected_property_name_suggestion}[/]?"
+        )
+        assert help_text.bullets[0].markup == expected_suggestion_message