diff --git a/server/pkg/sass/processor.go b/server/pkg/sass/processor.go
index 3aaad8f38..a92cc5d3a 100644
--- a/server/pkg/sass/processor.go
+++ b/server/pkg/sass/processor.go
@@ -58,7 +58,7 @@ func DefaultCSS(log *zap.Logger, customCSS string) string {
 
 func Transpile(transpiler *godartsass.Transpiler, log *zap.Logger, themeID, themeSASS, customCSS, sassDirPath string) (err error) {
 	// process root section
-	err = processSass(transpiler, log, SectionRoot, themeID, themeSASS, customCSS, sassDirPath)
+	err = processSass(transpiler, log, SectionRoot, themeID, themeSASS, "", sassDirPath)
 	if err != nil {
 		return err
 	}
diff --git a/server/system/service/stylesheet.go b/server/system/service/stylesheet.go
index 35b121c2f..724d9ff0a 100644
--- a/server/system/service/stylesheet.go
+++ b/server/system/service/stylesheet.go
@@ -65,10 +65,19 @@ func GenerateCSS(settings *types.AppSettings, sassDirPath string, log *zap.Logge
 func processCustomCSS(themeID string, customCSSMap map[string]string) (customCSS string) {
 	var stringsBuilder strings.Builder
 
+	// add theme mode on customCSS
+	if themeID == sass.DarkTheme {
+		stringsBuilder.WriteString(fmt.Sprintf("\n[data-color-mode=\"%s\"] {\n", themeID))
+	}
+
 	stringsBuilder.WriteString(customCSSMap[sass.GeneralTheme])
 	stringsBuilder.WriteString("\n")
 	stringsBuilder.WriteString(customCSSMap[themeID])
 
+	if themeID == sass.DarkTheme {
+		stringsBuilder.WriteString("}\n")
+	}
+
 	return stringsBuilder.String()
 }