refactor: update AddButton styling based on topic position and clean up CSS for root element

src/renderer/src/assets/styles/index.css

@@ -41,11 +41,11 @@ body,
   margin: 0;
 }
 
-/* #root {
+#root {
   display: flex;
   flex-direction: row;
   flex: 1;
-} */
+}
 
 body {
   display: flex;

src/renderer/src/pages/home/Tabs/components/AddButton.tsx

@@ -1,3 +1,4 @@
+import { useSettings } from '@renderer/hooks/useSettings'
 import type { ButtonProps } from 'antd'
 import { Button } from 'antd'
 import { PlusIcon } from 'lucide-react'
@@ -19,9 +20,12 @@ const StyledButton = styled(Button)`
 `
 
 const AddButton: FC<ButtonProps> = ({ ...props }) => {
+  const { topicPosition } = useSettings()
+
   return (
     <StyledButton
       {...props}
+      style={{ borderRadius: topicPosition === 'left' ? 20 : 8 }}
       type="text"
       onClick={props.onClick}
       icon={<PlusIcon size={16} style={{ flexShrink: 0 }} />}>