style(Sidebar): update border style

src/sidebar-item/index.less

@@ -1,6 +1,7 @@
 @import '../style/var';
 
 .van-sidebar-item {
+  position: relative;
   display: block;
   box-sizing: border-box;
   padding: @sidebar-padding;
@@ -10,19 +11,18 @@
   line-height: @sidebar-line-height;
   word-wrap: break-word;
   background-color: @sidebar-background-color;
-  border-left: 3px solid transparent;
   cursor: pointer;
   user-select: none;
 
+  &:active {
+    background-color: @sidebar-active-color;
+  }
+
   &__text {
     position: relative;
     display: inline-block;
   }
 
-  &:active {
-    background-color: @sidebar-active-color;
-  }
-
   &:not(:last-child)::after {
     border-bottom-width: 1px;
   }
@@ -30,16 +30,23 @@
   &--select {
     color: @sidebar-selected-text-color;
     font-weight: @sidebar-selected-font-weight;
-    border-color: @sidebar-selected-border-color;
-
-    &::after {
-      border-right-width: 1px;
-    }
 
     &,
     &:active {
       background-color: @sidebar-selected-background-color;
     }
+
+    &::before {
+      position: absolute;
+      top: 50%;
+      left: 0;
+      width: 4px;
+      height: 16px;
+      background-color: @sidebar-selected-border-color;
+      border-radius: @border-radius-md;
+      transform: translateY(-50%);
+      content: '';
+    }
   }
 
   &--disabled {