Add @tag-font-size

components/style/themes/default.less

@@ -303,6 +303,7 @@
 // --
 @tag-default-bg: #f3f3f3;
 @tag-default-color: @text-color;
+@tag-font-size: @font-size-base;
 
 // TimePicker
 // ---

components/tag/style/index.less

@@ -11,7 +11,7 @@
   border-radius: @border-radius-base;
   border: @border-width-base @border-style-base @border-color-split;
   background: @tag-default-bg;
-  font-size: @font-size-base;
+  font-size: @tag-font-size;
   transition: all 0.3s @ease-in-out-circ;
   opacity: 1;
   margin-right: 8px;