implement inline styles

sandbox/README.md

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+# Dev Sandbox
+
+This directory contains test code. None of the .py files here are garanteed to run or do anything useful, but you are welcome to look around.

sandbox/local_styles.css

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+App > View {
+  layout: dock;
+}
+
+Widget {
+  text: on blue;
+}

sandbox/local_styles.py

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+from textual.app import App
+from textual.widgets import Placeholder
+from textual.widget import Widget
+from textual import events
+
+
+class BasicApp(App):
+    """Sandbox application used for testing/development by Textual developers"""
+
+    def on_mount(self):
+        """Build layout here."""
+        self.mount(
+            header=Widget(),
+            content=Placeholder(),
+            footer=Widget(),
+            sidebar=Widget(),
+        )
+
+    async def on_key(self, event: events.Key) -> None:
+        await self.dispatch_key(event)
+
+    def key_a(self) -> bool | None:
+        self.query("#footer").set_styles(text="on magenta").refresh()
+
+        self.log(self["#footer"].styles.css)
+        self.bell()
+        self.refresh()
+
+    def key_b(self) -> bool | None:
+        self["#content"].set_styles("text: on magenta")
+
+
+BasicApp.run(css_file="local_styles.css", log="textual.log")