Fix content width (#1910)

* fix calculation for scrollbars

* added snapshot

* fix for name change

* snapshot

* fix for textual colors

* remove logs

* scrollbar logic

* scroll logic

* remove dead code

* snapshot tests

* scrollbar mechanism

* tidy

* demo tweak

* preset window size

* no need for repaint

* Restore repaint

* wait for idle on pause

* colors tweak

* remove wait for idle

* snapshot

* small sleep

* change stabilizer

* debug tweaks

* remove debug

* remove debug

* snapshot test

* docstring

* changelog

* add pause

tests/snapshot_tests/snapshot_apps/line_api_scrollbars.py

@@ -0,0 +1,54 @@
+from rich.text import Text
+
+from textual.app import App, ComposeResult
+from textual.containers import Vertical
+from textual.widget import Widget
+from textual.widgets import TextLog
+
+
+class MyWidget(Widget):
+    def render(self):
+        return Text(
+            "\n".join(f"{n} 0123456789" for n in range(20)),
+            no_wrap=True,
+            overflow="hidden",
+            justify="left",
+        )
+
+
+class ScrollViewApp(App):
+    CSS = """
+    Screen {
+        align: center middle;
+    }
+    
+    TextLog {
+        width:13;
+        height:10;        
+    }
+
+    Vertical{
+        width:13;
+        height: 10;
+        overflow: scroll;
+        overflow-x: auto;
+    }
+    MyWidget {
+        width:13;
+        height:auto;
+    }
+
+    """
+
+    def compose(self) -> ComposeResult:
+        yield TextLog()
+        yield Vertical(MyWidget())
+
+    def on_ready(self) -> None:
+        self.query_one(TextLog).write("\n".join(f"{n} 0123456789" for n in range(20)))
+        self.query_one(Vertical).scroll_end(animate=False)
+
+
+if __name__ == "__main__":
+    app = ScrollViewApp()
+    app.run()