Add wip test for user over widget css, use type alias

sandbox/darren/just_a_box.css

@@ -0,0 +1,11 @@
+Screen {
+    layout: dock;
+    height: 100%;
+}
+
+#box {
+    height: 50%;
+    width: 50%;
+    align: center middle;
+    background: green;
+}

sandbox/darren/just_a_box.py

@@ -0,0 +1,12 @@
+from textual.app import App, ComposeResult
+from textual.widgets import Static
+
+
+class JustABox(App):
+    def compose(self) -> ComposeResult:
+        yield Static("Hello, World!", id="box")
+
+
+if __name__ == "__main__":
+    app = JustABox(css_path="just_a_box.css", watch_css=True)
+    app.run()

src/textual/css/parse.py

@@ -7,6 +7,7 @@ from typing import Iterator, Iterable
 from rich import print
 
 from textual.css.errors import UnresolvedVariableError
+from textual.css.types import Specificity3
 from ._styles_builder import StylesBuilder, DeclarationError
 from .model import (
     Declaration,
@@ -20,7 +21,7 @@ from .styles import Styles
 from .tokenize import tokenize, tokenize_declarations, Token, tokenize_values
 from .tokenizer import EOFError, ReferencedBy
 
-SELECTOR_MAP: dict[str, tuple[SelectorType, tuple[int, int, int]]] = {
+SELECTOR_MAP: dict[str, tuple[SelectorType, Specificity3]] = {
     "selector": (SelectorType.TYPE, (0, 0, 1)),
     "selector_start": (SelectorType.TYPE, (0, 0, 1)),
     "selector_class": (SelectorType.CLASS, (0, 1, 0)),

tests/css/test_stylesheet.py

@@ -3,12 +3,15 @@ from typing import Any
 
 import pytest
 
+from tests.utilities.test_app import AppTest
+from textual.app import App, ComposeResult
 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
 from textual.dom import DOMNode
 from textual.geometry import Spacing
+from textual.widget import Widget
 
 
 def _make_stylesheet(css: str) -> Stylesheet:
@@ -101,6 +104,24 @@ def test_stylesheet_apply_empty_rulesets():
     stylesheet.apply(node)
 
 
+@pytest.mark.xfail(reason="wip")
+def test_stylesheet_apply_user_css_over_widget_css():
+    user_css = ".a {color: red;}"
+
+    class MyWidget(Widget):
+        CSS = ".a {color: blue;}"
+
+    node = MyWidget()
+    node.add_class("a")
+
+    print(node.styles.color)
+    stylesheet = _make_stylesheet(user_css)
+    stylesheet.apply(node)
+
+    assert node.styles.background == Color(0, 0, 255)
+    # TODO: On Tuesday - writing the tests for prioritising user CSS above widget CSS.
+
+
 @pytest.mark.parametrize(
     "css_value,expectation,expected_color",
     [