Improve support for declarations after nested rule sets.

Partially fixes #3999.

CHANGELOG.md

@@ -26,7 +26,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `SelectionList` option IDs are usable as soon as the widget is instantiated https://github.com/Textualize/textual/issues/3903
 - Fix issue with `Strip.crop` when crop window start aligned with strip end https://github.com/Textualize/textual/pull/3998
 - Fixed Strip.crop_extend https://github.com/Textualize/textual/pull/4011
-- Improve support for selector lists in nested CSS https://github.com/Textualize/textual/issues/3969
+- Improve support for selector lists in nested TCSS https://github.com/Textualize/textual/issues/3969
+- Improve support for rule declarations after nested TCSS rule sets https://github.com/Textualize/textual/issues/3999
 
 
 ## [0.47.1] - 2023-01-05

src/textual/css/tokenize.py

@@ -64,6 +64,7 @@ expect_root_nested = Expect(
     whitespace=r"\s+",
     comment_start=COMMENT_START,
     comment_line=COMMENT_LINE,
+    declaration_name=r"[a-zA-Z_\-]+\:",
     selector_start_id=r"\#" + IDENTIFIER,
     selector_start_class=r"\." + IDENTIFIER,
     selector_start_universal=r"\*",

tests/css/test_tokenize.py

@@ -987,3 +987,95 @@ def test_nested_css_selector_list_with_ampersand():
             location=(0, 36),
         ),
     ]
+
+
+def test_declaration_after_nested_declaration_set():
+    """Regression test for https://github.com/Textualize/textual/issues/3999."""
+    css = "Screen{Label{background:red;}background:green;}"
+    tokens = list(tokenize(css, ("", "")))
+    assert tokens == [
+        Token(
+            name="selector_start",
+            value="Screen",
+            read_from=("", ""),
+            code=css,
+            location=(0, 0),
+        ),
+        Token(
+            name="declaration_set_start",
+            value="{",
+            read_from=("", ""),
+            code=css,
+            location=(0, 6),
+        ),
+        Token(
+            name="selector_start",
+            value="Label",
+            read_from=("", ""),
+            code=css,
+            location=(0, 7),
+        ),
+        Token(
+            name="declaration_set_start",
+            value="{",
+            read_from=("", ""),
+            code=css,
+            location=(0, 12),
+        ),
+        Token(
+            name="declaration_name",
+            value="background:",
+            read_from=("", ""),
+            code=css,
+            location=(0, 13),
+        ),
+        Token(
+            name="token",
+            value="red",
+            read_from=("", ""),
+            code=css,
+            location=(0, 24),
+        ),
+        Token(
+            name="declaration_end",
+            value=";",
+            read_from=("", ""),
+            code=css,
+            location=(0, 27),
+        ),
+        Token(
+            name="declaration_set_end",
+            value="}",
+            read_from=("", ""),
+            code=css,
+            location=(0, 28),
+        ),
+        Token(
+            name="declaration_name",
+            value="background:",
+            read_from=("", ""),
+            code=css,
+            location=(0, 29),
+        ),
+        Token(
+            name="token",
+            value="green",
+            read_from=("", ""),
+            code=css,
+            location=(0, 40),
+        ),
+        Token(
+            name="declaration_end",
+            value=";",
+            read_from=("", ""),
+            code=css,
+            location=(0, 45),
+        ),
+        Token(
+            name="declaration_set_end",
+            value="}",
+            read_from=("", ""),
+            code=css,
+            location=(0, 46),
+        ),
+    ]