fix: add transparent window and fix CSS layout

src/styles/global.css

@@ -7,13 +7,17 @@
   box-sizing: border-box;
 }
 
-html, body, #app {
+html {
   height: 100%;
   width: 100%;
-  overflow: hidden;
 }
 
 body {
+  height: 100%;
+  width: 100%;
+  margin: 0;
+  padding: 0;
+  overflow: hidden;
   font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
   background: var(--bg-primary);
   color: var(--text-primary);
@@ -21,6 +25,11 @@ body {
   -moz-osx-font-smoothing: grayscale;
 }
 
+#app {
+  height: 100%;
+  width: 100%;
+}
+
 ::-webkit-scrollbar { width: 6px; height: 6px; }
 ::-webkit-scrollbar-track { background: transparent; }
 ::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.1); border-radius: 3px; }