feat(style): add component css variables

src/collapse-item/index.less

@@ -1,6 +1,16 @@
 @import './var.less';
 @import '../style/mixins/hairline';
 
+:root {
+  --van-collapse-item-transition-duration: @collapse-item-transition-duration;
+  --van-collapse-item-content-padding: @collapse-item-content-padding;
+  --van-collapse-item-content-font-size: @collapse-item-content-font-size;
+  --van-collapse-item-content-line-height: @collapse-item-content-line-height;
+  --van-collapse-item-content-text-color: @collapse-item-content-text-color;
+  --van-collapse-item-content-background-color: @collapse-item-content-background-color;
+  --van-collapse-item-title-disabled-color: @collapse-item-title-disabled-color;
+}
+
 .van-collapse-item {
   position: relative;
 
@@ -15,7 +25,7 @@
       // using translateZ to fix safari rendering issues
       // see: https://github.com/youzan/vant/issues/8608
       transform: rotate(90deg) translateZ(0);
-      transition: transform @collapse-item-transition-duration;
+      transition: transform var(--van-collapse-item-transition-duration);
     }
 
     &::after {
@@ -44,22 +54,22 @@
 
       &,
       & .van-cell__right-icon {
-        color: @collapse-item-title-disabled-color;
+        color: var(--van-collapse-item-title-disabled-color);
       }
     }
   }
 
   &__wrapper {
     overflow: hidden;
-    transition: height @collapse-item-transition-duration ease-in-out;
+    transition: height var(--van-collapse-item-transition-duration) ease-in-out;
     will-change: height;
   }
 
   &__content {
-    padding: @collapse-item-content-padding;
-    color: @collapse-item-content-text-color;
-    font-size: @collapse-item-content-font-size;
-    line-height: @collapse-item-content-line-height;
-    background-color: @collapse-item-content-background-color;
+    padding: var(--van-collapse-item-content-padding);
+    color: var(--van-collapse-item-content-text-color);
+    font-size: var(--van-collapse-item-content-font-size);
+    line-height: var(--van-collapse-item-content-line-height);
+    background-color: var(--van-collapse-item-content-background-color);
   }
 }