This is a working example and 9999 is the priority and you can adjust accordingly.

function wpdocs_custom_password_form() {
	global $post;

	$loginurl = site_url() . '/wp-login.php?action=postpass';
	$label = 'pwbox-' . ( ! empty( $post->ID ) ? $post->ID : rand() );

	ob_start();
	?>

	<style>
		.center-custom { margin: 0; position: absolute; top: 50%; left: 50%; -ms-transform: translate( -50%, -50% ); transform: translate( -50%, -50% ); }
		.post-password-label { color: #fff; }
		.post-password-class { width: 100% !important; }
		.post-password-class:focus { color: #fff !important; border-color: #fff !important; }
		@media only screen and ( max-width: 600px ) {
			.center-custom {
				width: 85%;
			}
		}
	</style>
	<div class="container-custom">			
		<form action="<?php echo esc_attr( $loginurl ) ?>" method="post" class="center-custom search-form" role="search">
			<label class="post-password-label"><?php esc_attr_e( "To view this protected post, enter the password below:" ) ?></label>
			<label for="<?php echo esc_attr( $label ) ?>" class="post-password-label"><?php _e( "Password:" ) ?></label>
			<input name="post_password" id="<?php echo esc_attr( $label ) ?>" class="input post-password-class" type="text" placeholder="Enter your access code provided by your concierge" />
			<input type="submit" name="Submit" class="button" value="<?php esc_attr_e( "Access" ) ?>" />			
		</form>
	</div>

	<?php
	return ob_get_clean();
}	
add_filter( 'the_password_form', 'wpdocs_custom_password_form', 9999 );