feat: update button variants and styles for improved consistency and accessibility

src/components/user/login-form.tsx

@@ -38,7 +38,7 @@ export default function LoginForm() {
         <Button type='submit' variant='primary'>
           Login
         </Button>
-        <Button type='submit' variant='outline'>
+        <Button type='submit' variant='outline_primary'>
           Sign Up
         </Button>
       </div>

src/components/user/sso-login-button.tsx

@@ -11,7 +11,7 @@ export default function SSOLogin({
 }) {
   return (
     <form
-      className='flex flex-col items-center gap-4 w-full'
+      className='flex flex-col items-center w-full'
       action={async () => {
         'use server';
         await signIn(provider);

src/components/user/theme-picker.tsx

@@ -18,7 +18,7 @@ export function ThemePicker() {
   return (
     <DropdownMenu>
       <DropdownMenuTrigger asChild>
-        <Button variant='outline' size='icon'>
+        <Button variant='outline_primary' size='icon'>
           <Sun className='h-[1.2rem] w-[1.2rem] rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0' />
           <Moon className='absolute h-[1.2rem] w-[1.2rem] rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100' />
           <span className='sr-only'>Toggle theme</span>