update datepicker style

style/components/datepicker/Calendar.less

@@ -156,6 +156,7 @@
     padding: 0;
     background: transparent;
     text-align: center;
+    transition: background 0.3s ease;
 
     &:hover {
       background: tint(@primary-color, 90%);

style/components/datepicker/DecadePanel.less

@@ -39,6 +39,7 @@
   line-height: 24px;
   padding: 0 6px;
   border-radius: 4px;
+  transition: background 0.3s ease;
 
   &:hover {
     background: tint(@primary-color, 90%);

style/components/datepicker/MonthPanel.less

@@ -39,6 +39,7 @@
   line-height: 24px;
   padding: 0 6px;
   border-radius: 4px;
+  transition: background 0.3s ease;
 
   &:hover {
     background: tint(@primary-color, 90%);

style/components/datepicker/TimePanel.less

@@ -54,6 +54,7 @@
   border-radius: 4px;
   margin: 0 auto;
   color: #666;
+  transition: background 0.3s ease;
 
   &:hover {
     background: tint(@primary-color, 90%);

style/components/datepicker/YearPanel.less

@@ -39,6 +39,7 @@
   line-height: 24px;
   padding: 0 6px;
   border-radius: 4px;
+  transition: background 0.3s ease;
 
   &:hover {
     background: tint(@primary-color, 90%);