improve style of color-picker

Author: elfman

browser/components/ColorPicker.styl

@@ -25,10 +25,12 @@
   vertical-align middle
   height 25px
   margin-top 2.5px
-  colorDefaultButton()
   border-radius 2px
-  border $ui-border
+  border none
   padding 0 5px
+  background-color $default-button-background
+  &:hover
+    background-color $default-button-background--hover
 .btn-confirm
   background-color #1EC38B
   &:hover