Restyle play+stop button to be Solara blue color

Author: rht

mesa/experimental/jupyter_viz.py

@@ -259,10 +259,13 @@ def do_set_playing(value):
         solara.Button(label="Step", color="primary", on_click=do_step)
         # This style is necessary so that the play widget has almost the same
         # height as typical Solara buttons.
-        solara.Style(
-            """
+        solara.Style("""
         .widget-play {
-            height: 30px;
+            height: 35px;
+        }
+        .widget-play button {
+            color: white;
+            background-color: #1976D2;  // Solara blue color
         }
         """
         )