fix(Slider): incorrect bar-height when vertical (#6065)

src/slider/index.less

@@ -3,6 +3,7 @@
 .van-slider {
   position: relative;
   width: 100%;
+  height: @slider-bar-height;
   background-color: @slider-inactive-background-color;
   border-radius: @border-radius-max;
   cursor: pointer;
@@ -19,7 +20,8 @@
 
   &__bar {
     position: relative;
-    height: @slider-bar-height;
+    width: 100%;
+    height: 100%;
     background-color: @slider-active-background-color;
     border-radius: inherit;
     transition: width @animation-duration-fast;
@@ -57,8 +59,17 @@
 
     .van-slider__button-wrapper {
       top: auto;
+      right: 50%;
       bottom: 0;
       transform: translate3d(50%, 50%, 0);
     }
+
+    // use pseudo element to expand click area
+    &::before {
+      top: 0;
+      right: -@padding-xs;
+      bottom: 0;
+      left: -@padding-xs;
+    }
   }
 }