[Doc] update neutral color variables (#2130)

packages/style/demo/index.vue

@@ -65,6 +65,8 @@ export default {
 </script>
 
 <style lang="less">
+@import '../../style/var';
+
 .demo-style {
   .van-ellipsis {
     font-size: 13px;
@@ -74,7 +76,7 @@ export default {
 
   .van-hairline--top {
     height: 30px;
-    background-color: #fff;
+    background-color: @white;
 
     &::after {
       top: 5px;
@@ -83,7 +85,7 @@ export default {
 
   .van-col {
     height: 50px;
-    color: #fff;
+    color: @white;
     font-size: 14px;
     border-radius: 3px;
     text-align: center;

packages/style/mixins/hairline.less

@@ -5,7 +5,7 @@
   box-sizing: border-box;
 }
 
-.hairline(@border-color: #eee) {
+.hairline(@border-color: #ebedf0) {
   .hairline-common();
 
   top: -50%;
@@ -16,7 +16,7 @@
   border: 0 solid @border-color;
 }
 
-.hairline-bottom(@border-color: #eee, @left: 0) {
+.hairline-bottom(@border-color: #ebedf0, @left: 0) {
   .hairline-common();
 
   left: @left;