By default, the platform does not have this option. You can use the following CSS code to change the shape of the Login button to a rectangle.

Please follow the steps below:

1. Go to BuddyBoss > Theme Options

2. Under Custom Codes, enable CSS

3. Append the following:

add_action('admin_head', 'my_custom_login_btn_rad');
function my_custom_login_btn_rad() {
  echo '<style>
    #loginform input#wp-submit { border-radius: 0!important; }
  </style>';
}

4. Save changes 

Note: Any modifications are considered as custom work already. Know more about our Support policy here: https://www.buddyboss.com/support-policy/