Remove white flash on desktop

I ask claude for some other suggestions for things to add here, and
I agree with 2 of them:

- Remove a white flash by setting a default collor of the window as
  black.
- Explicitly set the maximized state.

gui/assets/main.scss

@@ -16,6 +16,7 @@ body {
 }
 
 #main {
+  visibility: visible;
   height: 100vh;
   display: flex;
   flex-direction: column;

gui/src/main.rs

@@ -5,11 +5,15 @@ pub fn main() {
     Platform::init_logging();
     dioxus::LaunchBuilder::new()
         .with_cfg(desktop! {
-            dioxus::desktop::Config::new().with_window(
+            dioxus::desktop::Config::new()
+            .with_background_color((0, 0, 0, 255))
+            .with_custom_head("<style>html, body { background: black; } #main { visibility: hidden; }</style>".into())
+            .with_window(
                 dioxus::desktop::WindowBuilder::new()
                     .with_title("Mumble Web 2")
                     .with_min_inner_size(dioxus::desktop::LogicalSize::new(600.0, 300.0))
-                    .with_inner_size(dioxus::desktop::LogicalSize::new(900.0, 700.0)),
+                    .with_inner_size(dioxus::desktop::LogicalSize::new(900.0, 700.0))
+                    .with_maximized(false),
             )
         })
         .launch(app::app);