chore(Form): fix demo border

src/form/demo/FieldTypeArea.vue

@@ -1,10 +1,11 @@
 <template>
-  <div>
+  <div class="van-hairline--bottom">
     <van-field
       readonly
       clickable
       name="area"
       :value="value"
+      :border="false"
       :label="$t('picker')"
       :placeholder="$t('placeholder')"
       @click="showArea = true"

src/form/demo/FieldTypeDatetimePicker.vue

@@ -1,10 +1,11 @@
 <template>
-  <div>
+  <div class="van-hairline--bottom">
     <van-field
       readonly
       clickable
       name="datetimePicker"
       :value="value"
+      :border="false"
       :label="$t('label')"
       :placeholder="$t('placeholder')"
       @click="showPicker = true"

src/form/demo/FieldTypePicker.vue

@@ -1,10 +1,11 @@
 <template>
-  <div>
+  <div class="van-hairline--bottom">
     <van-field
       readonly
       clickable
       name="picker"
       :value="value"
+      :border="false"
       :label="$t('picker')"
       :placeholder="$t('placeholder')"
       @click="showPicker = true"

src/form/demo/index.vue

@@ -19,3 +19,14 @@ export default {
   },
 };
 </script>
+
+<style lang="less">
+.demo-form {
+  width: 100vw;
+  overflow: hidden;
+
+  .van-hairline--bottom::after {
+    margin-left: 16px;
+  }
+}
+</style>