[improvement] Actionsheet: use popup instead of mixin (#2806)

packages/actionsheet/index.less

@@ -1,23 +1,11 @@
 @import '../style/var';
 
 .van-actionsheet {
-  position: fixed;
-  left: 0;
-  right: 0;
-  bottom: 0;
-  color: @text-color;
   max-height: 90%;
-  overflow-y: auto;
-  -webkit-overflow-scrolling: touch;
-  background-color: @background-color;
-
-  &--withtitle {
-    background-color: @white;
-  }
+  color: @text-color;
 
   &__item,
   &__cancel {
-    height: 50px;
     line-height: 50px;
     font-size: 16px;
     text-align: center;
@@ -28,6 +16,10 @@
     }
   }
 
+  &__item {
+    height: 50px;
+  }
+
   &__item--disabled {
     color: @gray;
 
@@ -46,23 +38,26 @@
     display: inline-block;
   }
 
-  &__cancel {
-    margin-top: 10px;
+  &__cancel::before {
+    content: ' ';
+    display: block;
+    height: 10px;
+    background-color: @background-color;
   }
 
   &__header {
     font-size: 16px;
     line-height: 44px;
     text-align: center;
+  }
 
-    .van-icon-close {
-      top: 0;
-      right: 0;
-      padding: 0 15px;
-      font-size: 18px;
-      color: @gray-dark;
-      position: absolute;
-      line-height: inherit;
-    }
+  &__close {
+    top: 0;
+    right: 0;
+    padding: 0 15px;
+    font-size: 18px;
+    color: @gray-dark;
+    position: absolute;
+    line-height: inherit;
   }
 }