BI-157020 fix: 深色模式下clear的按钮带有背景色

packages/fineui/src/less/base/single/button/button.less

@@ -580,6 +580,10 @@ body .bi-button, #body .bi-button {
   .bi-button {
     background-color: @color-bi-background-button-theme-dark;
 
+    &.clear {
+      background-color: transparent;
+    }
+
     &.button-ignore {
       background-color: @color-bi-background-ignore-button-theme-dark;