Replace scss with bootstrap class

apps/app/src/client/components/PageControls/RagSearchButton.module.scss

@@ -5,11 +5,6 @@
 
 .btn-rag-search :global {
   @extend %btn-basis;
-  .growi-custom-icons {
-    font-size: 1.5em;
-    line-height: 1;
-    vertical-align: middle;
-  }
 }
 
 // == Colors

apps/app/src/client/components/PageControls/RagSearchButton.tsx

@@ -26,7 +26,7 @@ const RagSearchButton = (): JSX.Element => {
         onClick={ragSearchButtonClickHandler}
         data-testid="open-search-modal-button"
       >
-        <span className="growi-custom-icons">knowledge_assistant</span>
+        <span className="growi-custom-icons fs-4 align-middle lh-1">knowledge_assistant</span>
       </button>
     </NotAvailableForGuest>
   );

apps/app/src/features/openai/chat/components/AiChatModal/AiChatModal.module.scss

@@ -20,10 +20,6 @@
     color: growi-official-colors.$growi-ai-purple;
   }
 
-  .growi-custom-icons {
-    font-size: 1em;
-  }
-
   .btn-submit {
     @include btn-muted.colorize(bs.$purple, bs.$purple);
   }

apps/app/src/features/openai/chat/components/AiChatModal/AiChatModal.tsx

@@ -235,7 +235,7 @@ export const AiChatModal = (): JSX.Element => {
     <Modal size="lg" isOpen={isOpened} toggle={closeRagSearchModal} className={moduleClass} scrollable>
 
       <ModalHeader tag="h4" toggle={closeRagSearchModal} className="pe-4">
-        <span className="growi-custom-icons growi-ai-chat-icon me-3">knowledge_assistant</span>
+        <span className="growi-custom-icons growi-ai-chat-icon me-3 fs-4">knowledge_assistant</span>
         <span className="fw-bold">{t('modal_aichat.title')}</span>
         <span className="fs-5 text-body-secondary ms-3">{t('modal_aichat.title_beta_label')}</span>
       </ModalHeader>