render lines and scrollbars

src/textual/geometry.py

@@ -459,6 +459,11 @@ class Region(NamedTuple):
             height + expand_height * 2,
         )
 
+    def enlarge(self, size: tuple[int, int]) -> Region:
+        add_width, add_height = size
+        x, y, width, height = self
+        return Region(x, y, width + add_width, height + add_height)
+
     @lru_cache(maxsize=1024)
     def overlaps(self, other: Region) -> bool:
         """Check if another region overlaps this region.