Fix mobile menu blur and improve admin sidebar text contrast

src/lib/theme-css.ts

@@ -39,7 +39,7 @@ export function adminPaletteCss(admin: AdminPalette): string {
 	const parts: string[] = [
 		`--admin-sidebar-background:${admin.sidebar};`,
 		`--admin-sidebar-text-readable:${admin.sidebarText};`,
-		`--admin-sidebar-muted-readable:var(--admin-sidebar-text-readable);`,
+		`--admin-sidebar-muted-readable:color-mix(in srgb, var(--admin-sidebar-text-readable) 60%, transparent);`,
 		`--admin-input-text-readable:${readableColor(admin.text, [admin.canvas, admin.surface])};`,
 		`--admin-canvas:${admin.canvas};`,
 		`--admin-surface:${admin.surface};`,