style: enhance loading indicator and adjust Markdown component styling for consistency

web/app/components/rag-pipeline/components/panel/test-run/result/result-preview/index.tsx

     <>
       {isRunning && !outputs && (
         <div className='flex grow flex-col items-center justify-center gap-y-2 pb-20'>
-          <RiLoader2Line className='size-4 animate-spin' />
+          <RiLoader2Line className='size-4 animate-spin text-text-tertiary' />
           <div className='system-sm-regular text-text-tertiary'>{t('pipeline.result.resultPreview.loading')}</div>
         </div>
       )}

web/app/components/workflow/variable-inspect/display-content.tsx

         )}
         {viewMode === ViewMode.Preview && (
           previewType === PreviewType.Markdown
-            ? <Markdown className='grow overflow-auto rounded-lg !bg-white px-4 py-3' content={(mdString ?? '') as string} />
+            ? <Markdown className='grow overflow-auto rounded-lg px-4 py-3' content={(mdString ?? '') as string} />
             : <ChunkCardList
               chunkType={chunkType!}
               parentMode={parentMode}