Menu isn’t sticky | WordPress.org

This is the header.php code after i modified it:

 >
boldthemes_set_override();
boldthemes_header_init();
boldthemes_header_meta();
wp_head();
$body_style="";
if ( boldthemes_get_option( 'page_background' ) ) {
$body_style=" style="background-image:url(" . boldthemes_get_option( 'page_background' ) . ')"';
}
?>
 data-autoplay="" id="btBody" >


$content = get_post( MedicareTheme::$boldthemes_page_for_header_id );
$top_content = $content->post_content;
if ( $top_content != '' ) {
$top_content = apply_filters( 'the_content', $top_content );
$top_content = str_replace( ']]>', ']]>', $top_content );
}
echo '
' . $top_content .  '
';
} ?>

 'personal_blog')); ?>

	

Can I use custom CSS code to fix this?