Error messages for invalid colours in border property

sandbox/uber.css

@@ -12,6 +12,5 @@
   min-width: 80;
   background: dark_blue;
   padding: 2;
-  border-top: solid red ;
-  border-left: solid red ;
+  border: solid red;
 }

sandbox/uber.py

@@ -85,10 +85,7 @@ class BasicApp(App):
 
     def action_increase_margin(self):
         old_margin = self.focused.styles.margin
-        # new_margin = old_margin + (1,1,1)
-        # self.focused.styles.padding = (1, 1, 1)
-        self.focused.styles.color = "banana"
-        self.focused.styles.border
+        self.focused.styles.border = [("solid", "green"), ("dashed", "s")]
 
 
 BasicApp.run(css_file="uber.css", log="textual.log", log_verbosity=1)

src/textual/css/_help_text.py

@@ -4,6 +4,7 @@ import sys
 from dataclasses import dataclass
 
 from textual.css._help_renderables import Example, Bullet, HelpText
+from textual.css.constants import VALID_BORDER
 
 if sys.version_info >= (3, 8):
     from typing import Literal, Iterable
@@ -254,5 +255,48 @@ def border_property_help_text(
     property_name = _contextualize_property_name(property_name, context)
     return HelpText(
         summary=f"Invalid value for [i]{property_name}[/] property",
-        bullets=[*ContextSpecificBullets(inline=[Bullet("")]).get_by_context(context)],
+        bullets=[
+            *ContextSpecificBullets(
+                inline=[
+                    Bullet(
+                        f"In Python, set '{property_name}' using a tuple of the form (<bordertype>, <color>)",
+                        examples=[
+                            Example(
+                                f'widget.styles.{property_name} = ("solid", "red")'
+                            ),
+                            Example(
+                                f'widget.styles.{property_name} = ("round", #f0f0f0")'
+                            ),
+                            Example(
+                                f'widget.styles.{property_name} = [("dashed", "#f0f0f0"), ("solid", "blue")]  [dim]# Vertical, horizontal'
+                            ),
+                        ],
+                    ),
+                    Bullet(
+                        f"Valid values for <bordertype> are {friendly_list(VALID_BORDER)}"
+                    ),
+                    Bullet(
+                        f"Colors can be specified using hex, RGB, or ANSI color names"
+                    ),
+                ],
+                css=[
+                    Bullet(
+                        f"In Textual CSS, set '{property_name}' using a value of the form [i]<bordertype> <color>[/]",
+                        examples=[
+                            Example(f"{property_name}: solid red;"),
+                            Example(f"{property_name}: dashed #00ee22;"),
+                        ],
+                    ),
+                    Bullet(
+                        f"Valid values for <bordertype> are {friendly_list(VALID_BORDER)}"
+                    ),
+                    Bullet(
+                        f"Colors can be specified using hex, RGB, or ANSI color names"
+                    ),
+                    Bullet(
+                        f"To set border for a specific edge, use [i]border-top[/], [i]border-left[/], etc."
+                    ),
+                ],
+            ).get_by_context(context),
+        ],
     )

src/textual/css/_style_properties.py

@@ -14,7 +14,7 @@ from typing import Iterable, NamedTuple, TYPE_CHECKING, cast
 import rich.repr
 from rich.style import Style
 
-from ._help_text import scalar_help_text
+from ._help_text import scalar_help_text, border_property_help_text
 from .. import log
 from ._help_text import (
     spacing_wrong_number_of_values,
@@ -188,7 +188,15 @@ class BoxProperty:
             _type, color = border
             new_value = border
             if isinstance(color, str):
-                new_value = (_type, Color.parse(color))
+                try:
+                    new_value = (_type, Color.parse(color))
+                except ColorParseError as error:
+                    raise StyleValueError(
+                        str(error),
+                        help_text=border_property_help_text(
+                            self.name, context="inline"
+                        ),
+                    )
             elif isinstance(color, Color):
                 new_value = (_type, color)
             if obj.set_rule(self.name, new_value):

src/textual/css/_styles_builder.py

@@ -12,6 +12,7 @@ from ._help_text import (
     spacing_invalid_value,
     string_enum_help_text,
     color_property_help_text,
+    border_property_help_text,
 )
 from .constants import (
     VALID_ALIGN_HORIZONTAL,
@@ -391,15 +392,14 @@ class StylesBuilder:
                     try:
                         border_color = Color.parse(value)
                     except ColorParseError:
-                        # TODO: Raise specific error here
                         self.error(
-                            name, token, f"unexpected token {value!r} in declaration"
+                            name, token, border_property_help_text(name, context="css")
                         )
 
             elif token_name == "color":
                 border_color = Color.parse(value)
             else:
-                self.error(name, token, f"unexpected token {value!r} in declaration")
+                self.error(name, token, border_property_help_text(name, context="css"))
 
         return (border_type, border_color)