DEV: update a couple button classes (#23127)

app/assets/javascripts/select-kit/addon/components/dropdown-select-box.js

@@ -13,6 +13,7 @@ export default SingleSelectComponent.extend({
     caretDownIcon: "caret-down",
     showCaret: false,
     customStyle: null,
+    btnCustomClasses: null,
   },
 
   modifyComponentForRow() {

app/assets/javascripts/select-kit/addon/components/period-chooser/period-chooser-header.js

@@ -2,7 +2,7 @@ import DropdownSelectBoxHeaderComponent from "select-kit/components/dropdown-sel
 import discourseComputed from "discourse-common/utils/decorators";
 
 export default DropdownSelectBoxHeaderComponent.extend({
-  classNames: ["period-chooser-header"],
+  classNames: ["period-chooser-header", "btn-flat"],
 
   @discourseComputed("selectKit.isExpanded")
   caretIcon(isExpanded) {

plugins/chat/assets/javascripts/discourse/components/chat-message-actions-desktop.gjs

@@ -98,7 +98,12 @@ export default class ChatMessageActionsDesktop extends Component {
           }}
             <DropdownSelectBox
               @class="more-buttons secondary-actions"
-              @options={{hash icon="ellipsis-v" placement="left"}}
+              @options={{hash
+                icon="ellipsis-v"
+                placement="left"
+                customStyle="true"
+                btnCustomClasses="btn-flat"
+              }}
               @content={{this.messageInteractor.secondaryActions}}
               @onChange={{this.messageInteractor.handleSecondaryActions}}
             />