previews: remove central panel frame

This was adding padding we don't want

Signed-off-by: William Casarin <jb55@jb55.com>

src/ui/preview.rs

@@ -28,6 +28,8 @@ impl PreviewApp {
 
 impl eframe::App for PreviewApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
-        egui::CentralPanel::default().show(ctx, |ui| self.view.ui(ui));
+        egui::CentralPanel::default()
+            .frame(egui::Frame::none())
+            .show(ctx, |ui| self.view.ui(ui));
     }
 }