fix nested tab style

packages/theme-default/src/tabs.css

@@ -118,10 +118,10 @@
       position: relative;
     }
     @m card {
-      .el-tabs__nav .el-tabs__active-bar {
+      > .el-tabs__header .el-tabs__active-bar {
         display: none;
       }
-      .el-tabs__nav .el-tabs__item .el-icon-close {
+      > .el-tabs__header .el-tabs__item .el-icon-close {
         position: relative;
         font-size: 12px;
         width: 0;
@@ -133,7 +133,7 @@
         right: -2px;
         transform-origin: 100% 50%;
       }
-      .el-tabs__nav .el-tabs__item {
+      > .el-tabs__header .el-tabs__item {
         border: 1px solid transparent;
         transition: all .3s cubic-bezier(.645,.045,.355,1);
               
@@ -166,14 +166,14 @@
       border: 1px solid var(--color-base-gray);
       box-shadow: 0px 2px 4px 0px rgba(0,0,0,0.12), 0px 0px 6px 0px rgba(0,0,0,0.04);
 
-      &>.el-tabs__content {
+      >.el-tabs__content {
         padding: 15px;
       }
-      &>.el-tabs__header {
+      >.el-tabs__header {
         background-color: var(--color-extra-light-gray);
         margin: 0;
       }
-      &>.el-tabs__header>.el-tabs__item {
+      >.el-tabs__header .el-tabs__item {
         transition: all .3s cubic-bezier(.645,.045,.355,1);
         border: 1px solid transparent;
         border-top: 0;