feat: add @border-width-base var (#4595)

src/style/hairline.less

@@ -41,6 +41,6 @@
   }
 
   &--surround::after {
-    border-width: 1px;
+    border-width: @border-width-base;
   }
 }

src/style/var.less

@@ -14,7 +14,6 @@
 
 // Component Colors
 @text-color: #323233;
-@border-color: #ebedf0;
 @active-color: #f2f3f5;
 @background-color: #f8f8f8;
 @background-color-light: #fafafa;
@@ -27,19 +26,21 @@
 @padding-lg: @padding-base * 6;
 @padding-xl: @padding-base * 8;
 
-// Font Size
+// Font
 @font-size-xs: 10px;
 @font-size-sm: 12px;
 @font-size-md: 14px;
 @font-size-lg: 16px;
-
-// Font Weight
 @font-weight-bold: 500;
 
 // Animation
 @animation-duration-base: .3s;
 @animation-duration-fast: .2s;
 
+// Border
+@border-color: #ebedf0;
+@border-width-base: 1px;
+
 // ActionSheet
 @action-sheet-max-height: 90%;
 @action-sheet-header-height: 44px;