added color reference and docs

sandbox/will/box.css

@@ -0,0 +1,28 @@
+Screen {
+    background: white;
+    color:black;
+}
+
+#box1 {
+    width: 10;
+    height: 5;
+    background: red 40%;
+    box-sizing: content-box;
+}
+
+
+#box2 {
+    width: 10;
+    height: 5;
+    padding: 1;
+    background:blue 40%;
+    box-sizing: content-box;
+}
+
+#box3 {
+    width: 10;
+    height: 5;
+    background:green 40%;
+    border: heavy;
+    box-sizing: content-box;
+}

sandbox/will/box.py

@@ -0,0 +1,13 @@
+from textual.app import App
+from textual.widgets import Static
+
+class BoxApp(App):
+
+    def compose(self):
+        yield Static("0123456789", id="box1")
+        yield Static("0123456789", id="box2")
+        yield Static("0123456789", id="box3")
+
+
+app = BoxApp(css_path="box.css")
+app.run()