[css] Address PR feedback for our new "scrollbar-size" CSS properties

sandbox/basic.css

@@ -74,7 +74,7 @@ App > Screen {
 
 
 Tweet {
-  height: auto;
+  height: 12;
   width: 80;
  
   margin: 1 3;
@@ -90,6 +90,15 @@ Tweet {
   box-sizing: border-box;
 }
 
+Tweet.scrollbar-size-custom {
+  scrollbar-size-vertical: 2;
+}
+
+
+Tweet.scroll-horizontal {
+  scrollbar-size-horizontal: 2;
+}
+
 .scrollable {
   width: 80;
   overflow-y: scroll;
@@ -114,12 +123,15 @@ TweetHeader {
 }
 
 TweetBody {  
-  width: 130%;
+  width: 100%;
   background: $panel;
   color: $text-panel;
   height: auto; 
   padding: 0 1 0 0; 
- 
+}
+
+Tweet.scroll-horizontal TweetBody {
+  width: 130%;
 }
 
 .button {

sandbox/basic.py

@@ -107,15 +107,15 @@ class BasicApp(App, css_path="basic.css"):
                 ),
             ),
             content=Widget(
-                Tweet(TweetBody(), classes="scrollbar-size-test"),
+                Tweet(TweetBody()),
                 Widget(
                     Static(Syntax(CODE, "python"), classes="code"),
                     classes="scrollable",
                 ),
                 Error(),
-                Tweet(TweetBody()),
+                Tweet(TweetBody(), classes="scrollbar-size-custom"),
                 Warning(),
-                Tweet(TweetBody()),
+                Tweet(TweetBody(), classes="scroll-horizontal"),
                 Success(),
             ),
             footer=Widget(),

src/textual/css/_help_text.py

@@ -646,7 +646,9 @@ def scrollbar_size_property_help_text(context: StylingContext) -> HelpText:
                     ),
                 ],
             ).get_by_context(context),
-            Bullet("<horizontal> and <vertical> must be positive integers"),
+            Bullet(
+                "<horizontal> and <vertical> must be positive integers, greater than zero"
+            ),
         ],
     )
 
@@ -664,7 +666,7 @@ def scrollbar_size_single_axis_help_text(property_name: str) -> HelpText:
         summary=f"Invalid value for [i]{property_name}[/]",
         bullets=[
             Bullet(
-                markup=f"The [i]{property_name}[/] property can only be set to a positive integer",
+                markup=f"The [i]{property_name}[/] property can only be set to a positive integer, greather than zero",
                 examples=[
                     Example(f"{property_name}: 2;"),
                 ],

src/textual/css/_styles_builder.py

@@ -802,7 +802,12 @@ class StylesBuilder:
             if token2.name != "number" or not token2.value.isdigit():
                 scrollbar_size_error(name, token2)
 
-            horizontal, vertical = int(token1.value), int(token2.value)
+            horizontal = int(token1.value)
+            if horizontal == 0:
+                scrollbar_size_error(name, token1)
+            vertical = int(token2.value)
+            if vertical == 0:
+                scrollbar_size_error(name, token2)
             self.styles._rules["scrollbar_size_horizontal"] = horizontal
             self.styles._rules["scrollbar_size_vertical"] = vertical
 
@@ -815,7 +820,10 @@ class StylesBuilder:
             token = tokens[0]
             if token.name != "number" or not token.value.isdigit():
                 self.error(name, token, scrollbar_size_single_axis_help_text(name))
-            self.styles._rules["scrollbar_size_vertical"] = int(token.value)
+            value = int(token.value)
+            if value == 0:
+                self.error(name, token, scrollbar_size_single_axis_help_text(name))
+            self.styles._rules["scrollbar_size_vertical"] = value
 
     def process_scrollbar_size_horizontal(self, name: str, tokens: list[Token]) -> None:
         if not tokens:
@@ -826,7 +834,10 @@ class StylesBuilder:
             token = tokens[0]
             if token.name != "number" or not token.value.isdigit():
                 self.error(name, token, scrollbar_size_single_axis_help_text(name))
-            self.styles._rules["scrollbar_size_horizontal"] = int(token.value)
+            value = int(token.value)
+            if value == 0:
+                self.error(name, token, scrollbar_size_single_axis_help_text(name))
+            self.styles._rules["scrollbar_size_horizontal"] = value
 
     def _get_suggested_property_name_for_rule(self, rule_name: str) -> str | None:
         """

src/textual/widget.py

@@ -288,13 +288,9 @@ class Widget(DOMNode):
 
         if self._vertical_scrollbar is not None:
             return self._vertical_scrollbar
-        thickness = (
+        (vertical_scrollbar_thickness, _) = self._get_scrollbar_thicknesses()
-            1
-            if self.styles.scrollbar_size_vertical is None
-            else int(self.styles.scrollbar_size_vertical.value)
-        )
         self._vertical_scrollbar = scroll_bar = ScrollBar(
-            vertical=True, name="vertical", thickness=thickness
+            vertical=True, name="vertical", thickness=vertical_scrollbar_thickness
         )
         self.app.start_widget(self, scroll_bar)
         return scroll_bar
@@ -310,13 +306,9 @@ class Widget(DOMNode):
 
         if self._horizontal_scrollbar is not None:
             return self._horizontal_scrollbar
-        thickness = (
+        (_, horizontal_scrollbar_thickness) = self._get_scrollbar_thicknesses()
-            1
-            if self.styles.scrollbar_size_horizontal is None
-            else int(self.styles.scrollbar_size_horizontal.value)
-        )
         self._horizontal_scrollbar = scroll_bar = ScrollBar(
-            vertical=False, name="horizontal", thickness=thickness
+            vertical=False, name="horizontal", thickness=horizontal_scrollbar_thickness
         )
 
         self.app.start_widget(self, scroll_bar)
@@ -330,9 +322,6 @@ class Widget(DOMNode):
         styles = self.styles
         overflow_x = styles.overflow_x
         overflow_y = styles.overflow_y
-        scrollbar_size_horizontal = styles.scrollbar_size_horizontal
-        scrollbar_size_vertical = styles.scrollbar_size_vertical
-        overflow_y = styles.overflow_y
         width, height = self.container_size
 
         show_horizontal = self.show_horizontal_scrollbar
@@ -342,11 +331,6 @@ class Widget(DOMNode):
             show_horizontal = True
         elif overflow_x == "auto":
             show_horizontal = self.virtual_size.width > width
-        if (
-            scrollbar_size_horizontal is not None
-            and scrollbar_size_horizontal.value == 0
-        ):
-            show_horizontal = False
 
         show_vertical = self.show_vertical_scrollbar
         if overflow_y == "hidden":
@@ -355,8 +339,6 @@ class Widget(DOMNode):
             show_vertical = True
         elif overflow_y == "auto":
             show_vertical = self.virtual_size.height > height
-        if scrollbar_size_vertical is not None and scrollbar_size_vertical.value == 0:
-            show_vertical = False
 
         self.show_horizontal_scrollbar = show_horizontal
         self.show_vertical_scrollbar = show_vertical

tests/test_integration_layout.py

@@ -266,8 +266,6 @@ async def test_border_edge_types_impact_on_widget_size(
             ("overflow: auto", "scrollbar-size: 3 3"),
             Size(20, 17),
         ],
-        # edge case: scrollbars should not be displayed at all if their size is set to 0
-        [Size(30, 30), ("overflow: auto", "scrollbar-size: 0 0"), Size(20, 20)],
     ),
 )
 async def test_scrollbar_size_impact_on_the_layout(