style: add styling to disk module

resources/style.css

@@ -69,6 +69,7 @@ window#waybar.chromium {
 #battery,
 #cpu,
 #memory,
+#disk,
 #temperature,
 #backlight,
 #network,
@@ -142,6 +143,10 @@ label:focus {
     background-color: #9b59b6;
 }
 
+#disk {
+    background-color: #964B00;
+}
+
 #backlight {
     background-color: #90b1b1;
 }