Set DataTable default style to max-height: 100% (#2974)

* Make the default max-height of a DataTable 100%

See #2959

* Fix the demo

Adding `max-height: 100%;` to DataTable has worked everywhere, except in the
demo, where it makes the table just plain flat out disappear. It looks like
it's down to a bug in Textual's CSS, possibly. This fixes the demo for now,
and a standalone issue will follow that dives into what's going on with this
particular combination of container and datatable styling.

* Update the ChangeLog

* Update the FAQ

CHANGELOG.md

@@ -24,6 +24,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed issue with tabs in TextLog https://github.com/Textualize/textual/issues/3007
 
 
+### Changed
+
+- Breaking change: the default style of a `DataTable` now has `max-height: 100%` https://github.com/Textualize/textual/issues/2959
+
 ## [0.30.0] - 2023-07-17
 
 ### Added

FAQ.md

@@ -265,6 +265,8 @@ If scrolling in your `DataTable` is _apparently_ broken, it may be because your
 This means that the table will be sized to fit its rows without scrolling, which may cause the *container* (typically the screen) to scroll.
 If you would like the table itself to scroll, set the height to something other than `auto`, like `100%`.
 
+**NOTE:** As of Textual v0.31.0 the `max-height` of a `DataTable` is set to `100%`, this will mean that the above is no longer the default experience.
+
 <hr>
 
 Generated by [FAQtory](https://github.com/willmcgugan/faqtory)

questions/datatable-doesnt-scroll.question.md

@@ -8,3 +8,5 @@ alt_titles:
 If scrolling in your `DataTable` is _apparently_ broken, it may be because your `DataTable` is using the default value of `height: auto`.
 This means that the table will be sized to fit its rows without scrolling, which may cause the *container* (typically the screen) to scroll.
 If you would like the table itself to scroll, set the height to something other than `auto`, like `100%`.
+
+**NOTE:** As of Textual v0.31.0 the `max-height` of a `DataTable` is set to `100%`, this will mean that the above is no longer the default experience.

src/textual/demo.css

@@ -208,6 +208,7 @@ LocationLink:hover {
 
 DataTable {
     height: 16;
+    max-height: 16;
 }
 
 

src/textual/widgets/_data_table.py

@@ -251,6 +251,7 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
         background: $surface ;
         color: $text;
         height: auto;
+        max-height: 100%;
     }
     DataTable > .datatable--header {
         text-style: bold;