Warning: Cannot modify header information

Hello, today i was installing a wordpress to my hosting. And when i install a themes, i got this error message :

Warning: Cannot modify header information – headers already sent by (output started at /home/jetilnfc/public_html/wp-content/themes/Animesaber style/functions.php:36) in /home/jetilnfc/public_html/wp-includes/pluggable.php on line 875

And this is my function.php code :

<?php
    function animesaber_widgets() {
      register_sidebar( array(
        'name' => 'Sidebar onside',
        'id' => 'sidebar-onside',
        'description' => 'Sidebar yang terletak di bagian kanan',
        'before_widget' => '<div class="widget">',
        'after_widget' => '</div>',
        'before_title' => '<h3 class="widgettitle">',
        'after_title' => '</h3>',
      ) );
      register_sidebar( array(
        'name' => 'Sidebar footer',
        'id' => 'sidebar-footer',
        'description' => 'Sidebar yang terletak di bagian bawah',
        'before_widget' => '<div class="widget2">',
        'after_widget' => '</div>',
        'before_title' => '<h3 class="widgettitle">',
        'after_title' => '</h3>',
      ) );
       register_sidebar( array(
        'name' => 'Sidebar footer 2',
        'id' => 'sidebar-footer2',
        'description' => 'Sidebar yang terletak di bagian bawah kanan',
        'before_widget' => '<div class="widget3">',
        'after_widget' => '</div>',
        'before_title' => '<h3 class="widgettitle">',
        'after_title' => '</h3>',
      ) );
    }
add_action( 'widgets_init', 'animesaber_widgets' );
add_theme_support( 'post-thumbnails' );
    set_post_thumbnail_size( 210, 180, true );
?>

Its very simple but why i got those error?
Can someone please help, i wil really appreciate it. Thanks!