diff --git a/internal/system/box.go b/internal/system/box.go
index 807b84b..3aeb777 100644
--- a/internal/system/box.go
+++ b/internal/system/box.go
@@ -130,11 +130,15 @@ func (this *box) Tag (tag string) bool {
 }
 
 func (this *box) SetTag (tag string, on bool) {
+	wasOn := this.tags.Has(tag)
 	if on {
 		this.tags.Add(tag)
 	} else {
 		delete(this.tags, tag)
 	}
+	if wasOn != on {
+		this.invalidateStyle()
+	}
 }
 
 func (this *box) SetAttr (attr tomo.Attr) {