fix(components): [tab] fix style when tab position is bottom (element-plus#18425)

* fix(components): [tab] fix style when tab position is bottom

* style: remove redundant style

Author: btea

packages/theme-chalk/src/tabs.scss

@@ -29,6 +29,9 @@
       transform getCssVar('transition-duration')
         getCssVar('transition-function-ease-in-out-bezier');
     list-style: none;
+    &.is-bottom {
+      bottom: auto;
+    }
   }
   @include e(new-tab) {
     display: flex;
@@ -81,6 +84,11 @@
       z-index: getCssVar('index-normal');
     }
 
+    &.is-bottom::after {
+      top: 0;
+      bottom: auto;
+    }
+
     @include when(scrollable) {
       padding: 0 20px;
       box-sizing: border-box;