Border style (#2292)

* border styles

* docs for border styles

* fix tests

* tests

* tests and docs

* changelog

* implement auto

* style information fix

docs/styles/border_title_style.md

@@ -0,0 +1,35 @@
+# Border-title-style
+
+The `border-title-style` style sets the text style of the [border_title][textual.widget.Widget.border_title].
+
+
+## Syntax
+
+--8<-- "docs/snippets/syntax_block_start.md"
+border-title-style: <a href="../../css_types/text_style">&lt;text-style&gt;</a>;
+--8<-- "docs/snippets/syntax_block_end.md"
+
+
+
+## Example
+
+--8<-- "docs/snippets/border_title_color.md"
+
+
+## CSS
+
+```sass
+border-title-style: bold underline;
+```
+
+## Python
+
+```python
+widget.styles.border_title_style = "bold underline"
+```
+
+
+
+## See also
+
+--8<-- "docs/snippets/see_also_border.md"