feat: support custom background colors for sidebar and header (#4151)

* feat: support custom background colors for sidebar and header

* fix: type error

docs/src/guide/essentials/settings.md

@@ -260,6 +260,7 @@ const defaultPreferences: Preferences = {
     colorWarning: 'hsl(42 84% 61%)',
     mode: 'dark',
     radius: '0.5',
+    semiDarkHeader: false,
     semiDarkMenu: true,
   },
   transition: {
@@ -452,6 +453,8 @@ interface ThemePreferences {
   mode: ThemeModeType;
   /** 圆角 */
   radius: string;
+  /** 是否开启半深色header（只在theme='light'时生效） */
+  semiDarkHeader: boolean;
   /** 是否开启半深色菜单（只在theme='light'时生效） */
   semiDarkMenu: boolean;
 }