don't use chainmap

Author: willmcgugan

src/textual/css/styles.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-from collections import ChainMap
 from dataclasses import dataclass, field
 from functools import lru_cache, partial
 from operator import attrgetter
@@ -1103,9 +1102,6 @@ def __init__(self, node: DOMNode, base: Styles, inline_styles: Styles) -> None:
         self._updates: int = 0
         self._rich_style: tuple[int, Style] | None = None
         self._gutter: tuple[int, Spacing] | None = None
-        self._render_rules = ChainMap(inline_styles._rules, base._rules)
-        self.get_rule = self._render_rules.get  # type: ignore[assignment]
-        self.has_rule = self._render_rules.__contains__  # type: ignore[assignment]
 
     def __eq__(self, other: object) -> bool:
         if isinstance(other, RenderStyles):
@@ -1226,10 +1222,19 @@ def reset(self) -> None:
         self._inline_styles.reset()
         self._updates += 1
 
+    def has_rule(self, rule: str) -> bool:
+        """Check if a rule has been set."""
+        return self._inline_styles.has_rule(rule) or self._base_styles.has_rule(rule)
+
     def set_rule(self, rule: str, value: object | None) -> bool:
         self._updates += 1
         return self._inline_styles.set_rule(rule, value)
 
+    def get_rule(self, rule: str, default: object = None) -> object:
+        if self._inline_styles.has_rule(rule):
+            return self._inline_styles.get_rule(rule, default)
+        return self._base_styles.get_rule(rule, default)
+
     def clear_rule(self, rule_name: str) -> bool:
         """Clear a rule (from inline)."""
         self._updates += 1