Tabs: fix a close button style overwriting bug

packages/theme-default/src/tabs.css

@@ -52,7 +52,7 @@
       .el-tabs__active-bar {
         display: none;
       }
-      & .el-icon-close {
+      & .el-tabs__item .el-icon-close {
         font-size: 12px;
         vertical-align: middle;
         line-height: 15px;