Dark theme: add styles for ec-symptom-picker

Change-Id: I838bf6f378704055cad7533f4d18f359697c479e
diff --git a/src/static/css/ccdarktheme.css b/src/static/css/ccdarktheme.css
index 6857eb8..2f4fb14 100644
--- a/src/static/css/ccdarktheme.css
+++ b/src/static/css/ccdarktheme.css
@@ -201,8 +201,9 @@
   color: #fbbc04!important;
 }
 
-/* ec-work-state-picker */
-ec-work-state-picker > button {
+/* ec-work-state-picker and ec-symptom-picker */
+ec-work-state-picker > button,
+    ec-symptom-picker > button {
   color: var(--TWPT-secondary-text)!important;
   background-color: var(--TWPT-button-background)!important;
   border-color: var(--TWPT-subtle-border)!important;