style: format code with Prettier and remove unused code

Change-Id: I382f39d142cfa29f192447b0d2c6d48e113327b4
diff --git a/popup.css b/popup.css
index 620d6a8..bd8c062 100644
--- a/popup.css
+++ b/popup.css
@@ -9,17 +9,17 @@
   width: 150px;
 }
 div#options div.option {
-  text-align:center;
-  padding:8px;
-  background-color:#EEEEEE;
+  text-align: center;
+  padding: 8px;
+  background-color: #eeeeee;
   border-bottom: solid 1px gray;
   cursor: pointer;
 }
 div#options div.option:hover {
-  background-color:#DDDDDD;
+  background-color: #dddddd;
 }
 div#options div.option:active {
-  background-color:#CCCCCC;
+  background-color: #cccccc;
 }
 div#options div.option:last-child {
   border-bottom: none;