Merge pull request #727 from Textualize/default-css

Default css

sandbox/will/add_remove.py

@@ -11,7 +11,7 @@ class Thing(Static):
 
 
 class AddRemoveApp(App):
-    CSS = """
+    DEFAULT_CSS = """
     #buttons {
         dock: top;
         height: auto;       

sandbox/will/center.py

@@ -3,7 +3,7 @@ from textual.widgets import Static
 
 
 class CenterApp(App):
-    CSS = """
+    DEFAULT_CSS = """
     
     CenterApp Screen {
         layout: center;

sandbox/will/center2.py

@@ -4,7 +4,7 @@ from textual.widgets import Static
 
 
 class CenterApp(App):
-    CSS = """
+    DEFAULT_CSS = """
 
     #sidebar {
         dock: left;

sandbox/will/just_a_box.py

@@ -10,7 +10,7 @@ from textual.widget import Widget
 
 
 class Box(Widget, can_focus=True):
-    CSS = "#box {background: blue;}"
+    DEFAULT_CSS = "#box {background: blue;}"
 
     def render(self) -> RenderableType:
         return Panel("Box")

sandbox/will/screens.py

@@ -21,7 +21,7 @@ class NewScreen(Screen):
 
 
 class ScreenApp(App):
-    CSS = """
+    DEFAULT_CSS = """
     ScreenApp Screen {
         background: #111144;
         color: white;

sandbox/will/tree.py

@@ -5,7 +5,7 @@ from textual.widgets import DirectoryTree
 
 
 class TreeApp(App):
-    CSS = """
+    DEFAULT_CSS = """
     Screen {
         overflow: auto;