feat(tree-menu): [tree-menu] add dark theme (#2998)

Author: wuyiping0628

examples/sites/demos/pc/app/tree-menu/tree-menu-slot-composition-api.vue

@@ -120,7 +120,6 @@ const treeData = ref([
 <style scoped>
 .tree-menu-demo a,
 .tree-menu-demo a:hover {
-  color: #333;
   text-decoration: none;
 }
 .custom-icon {

examples/sites/demos/pc/app/tree-menu/tree-menu-slot.vue

@@ -122,7 +122,6 @@ export default {
 <style scoped>
 .tree-menu-demo a,
 .tree-menu-demo a:hover {
-  color: #333;
   text-decoration: none;
 }
 .custom-icon {

packages/theme/src/tree-menu/index.less

@@ -39,7 +39,7 @@
     border-radius: 50%;
     font-size: 18px;
     line-height: 18px;
-    background-color: #fff;
+    background-color: var(--tv-TreeMenu-toggle-button-background-color);
     box-shadow: 0 2px 4px 0px rgba(0, 0, 0, 0.06);
     border: 1px solid var(--tv-TreeMenu-border-color);
 
@@ -67,7 +67,7 @@
     bottom: 0;
     left: 0;
     width: 100%;
-    background-color: #fff;
+    background-color: var(--tv-TreeMenu-toggle-button-background-color);
 
     svg {
       width: 22px;

packages/theme/src/tree-menu/vars.less

@@ -75,4 +75,6 @@
   --tv-TreeMenu-scrollbar-margin-right: var(--tv-space-base);
   // 名称hover文字字重
   --tv-TreeMenu-node-name-hover-font-weight: var(--tv-font-weight-bold);
+  // 左侧折叠图标背景色
+  --tv-TreeMenu-toggle-button-background-color: var(--tv-color-bg-3);
 }