feat(themes): crossfade theme changes and fix window overflow

Crossfade user-selected themes, keep the theme volume popover open while
dragging its slider, and clip the fixed app shell so oversized theme layers
cannot create page scrollbars on Windows. Remove the redundant in-use badge
from the active theme card.

src/app.css

@@ -162,7 +162,10 @@
     -ms-user-select: none;
     user-select: none;
   }
-  html {
+  html,
+  body {
+    height: 100%;
+    overflow: hidden;
     overscroll-behavior: none;
   }
   body {
@@ -197,3 +200,31 @@ video::-webkit-media-controls-overlay-enclosure {
   width: 0 !important;
   height: 0 !important;
 }
+
+/* Crossfade the rendered page when switching themes via the View Transitions API. */
+::view-transition-old(root) {
+  animation: 320ms cubic-bezier(0.4, 0, 0.2, 1) both theme-crossfade-out;
+}
+
+::view-transition-new(root) {
+  animation: 320ms cubic-bezier(0.4, 0, 0.2, 1) both theme-crossfade-in;
+}
+
+@keyframes theme-crossfade-out {
+  to {
+    opacity: 0;
+  }
+}
+
+@keyframes theme-crossfade-in {
+  from {
+    opacity: 0;
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  ::view-transition-old(root),
+  ::view-transition-new(root) {
+    animation: none !important;
+  }
+}

src/lib/components/ui/titlebar/titlebar.svelte

@@ -16,6 +16,34 @@
 
   const iconSet = $derived($active_custom_theme?.definition?.iconSet ?? DEFAULT_THEME_ICON_SET);
 
+  let volumeOpen = $state(false);
+  let volumeDragging = $state(false);
+  let volumeControl: HTMLDivElement | undefined = $state();
+
+  function openVolume() {
+    volumeOpen = true;
+  }
+
+  function closeVolume() {
+    if (!volumeDragging) volumeOpen = false;
+  }
+
+  function startVolumeDrag(event: PointerEvent) {
+    if (event.button !== 0) return;
+    volumeDragging = true;
+    volumeOpen = true;
+  }
+
+  function endVolumeDrag(event: PointerEvent) {
+    if (!volumeDragging) return;
+    volumeDragging = false;
+
+    const element = document.elementFromPoint(event.clientX, event.clientY);
+    if (!element || !volumeControl?.contains(element)) {
+      volumeOpen = false;
+    }
+  }
+
   onMount(() => {
     const appWindow = getCurrentWindow();
 
@@ -26,9 +54,18 @@
   });
 </script>
 
+<svelte:window onpointerup={endVolumeDrag} onpointercancel={endVolumeDrag} />
+
 <div data-tauri-drag-region class="titlebar z-[100]" class:macos-window={$platform === 'macos'}>
   {#if $custom_theme_audio_playing || ($active_custom_theme && $active_custom_theme.name !== 'Default')}
-    <div class="relative flex items-center justify-center group">
+    <div
+      class="relative flex items-center justify-center group"
+      role="group"
+      aria-label="Theme volume"
+      bind:this={volumeControl}
+      onpointerenter={openVolume}
+      onpointerleave={closeVolume}
+    >
       <div class="relative flex items-center justify-center p-1 cursor-pointer">
         <div
           class="absolute inset-0 bg-background rounded
@@ -51,8 +88,9 @@
 
       <div
         class="absolute top-full right-0 translate-x-[7px]
-           opacity-0 invisible pointer-events-none -translate-y-2
-           group-hover:opacity-100 group-hover:visible group-hover:pointer-events-auto group-hover:translate-y-0
+           {volumeOpen
+          ? 'opacity-100 visible pointer-events-auto translate-y-0'
+          : 'opacity-0 invisible pointer-events-none -translate-y-2'}
            {$reduceAnimations ? '' : 'transition-all duration-200 ease-out'}
            z-50"
       >
@@ -68,6 +106,7 @@
             max="1"
             step="0.01"
             bind:value={$custom_theme_volume}
+            onpointerdown={startVolumeDrag}
             oninput={() => {
               config.value<number>('volume').set($custom_theme_volume);
             }}

src/lib/theme/themes.ts

@@ -7,6 +7,7 @@ import { convertFileSrc, invoke } from '@tauri-apps/api/core';
 import { listen } from '@tauri-apps/api/event';
 import * as path from '@tauri-apps/api/path';
 import * as fs from '@tauri-apps/plugin-fs';
+import { tick } from 'svelte';
 
 export type Theme = {
   folder_name: string;
@@ -486,7 +487,18 @@ export const downloadTheme = async (
   return { success: true };
 };
 
-export const loadTheme = async (theme: Theme, themeContainer: HTMLElement, volume = 0.15) => {
+type LoadThemeOptions = {
+  /** Crossfade the rendered page when switching themes. */
+  animate?: boolean;
+};
+
+export const loadTheme = async (
+  theme: Theme,
+  themeContainer: HTMLElement,
+  volume = 0.15,
+  options: LoadThemeOptions = {}
+) => {
+  const applyTheme = async () => {
     // Theme media is buffered as blob URLs; the previous theme's URLs are no
     // longer needed once it is replaced.
     clearThemeMediaCache();
@@ -516,6 +528,28 @@ export const loadTheme = async (theme: Theme, themeContainer: HTMLElement, volum
     void invoke('unlock_media_autoplay').catch(() => {});
   };
 
+  const canAnimate =
+    options.animate &&
+    typeof document !== 'undefined' &&
+    typeof document.startViewTransition === 'function';
+
+  if (!canAnimate) {
+    await applyTheme();
+    return;
+  }
+
+  const transition = document.startViewTransition(async () => {
+    await applyTheme();
+    // Let Svelte paint the new theme before the transition takes its snapshot.
+    await tick();
+  });
+
+  // Theme activation must not wait for, or fail because of, the visual
+  // transition. `finished` can reject when a transition is skipped.
+  void transition.finished.catch(() => {});
+  await transition.updateCallbackDone;
+};
+
 export const deleteTheme = async (themeToUninstall: Theme) => {
   if (themeToUninstall.status !== 'installed') {
     return false;

src/routes/+layout.svelte

@@ -583,6 +583,7 @@
   </AlertDialog.Root>
 
   <main
+    class="relative h-screen w-full overflow-hidden"
     use:appActivity
     use:themeMediaSuspension
     use:themeParallax={{

src/screens/Launch.svelte

@@ -526,7 +526,9 @@
       return;
     }
 
-    loadTheme(theme, $custom_theme_container, $custom_theme_volume);
+    await loadTheme(theme, $custom_theme_container, $custom_theme_volume, {
+      animate: !$reduceAnimations,
+    });
     await config.value<string>('theme').set(theme.name);
   };
 
@@ -4511,9 +4513,6 @@
                                 <div
                                   class="absolute top-1.5 left-1.5 flex max-w-[calc(100%-4.5rem)] flex-wrap items-center gap-1"
                                 >
-                                  {#if isActive}
-                                    <Badge class="text-[9px]">In use</Badge>
-                                  {/if}
                                   {#if theme.name !== 'Default' && theme.folder_name !== 'default' && theme.apiVersion}
                                     <Badge
                                       variant="secondary"