searchform.php override not working

I’m taking a Udemy class to learn how to make WordPress plugins and themes. The video I’m on is having me override the default search widget with a custom one via searchform.php. From what I’ve gathered, this file should automatically be loaded with the rest of the theme as long as I have followed these steps:

/theme_dir/functions.php

/* Some other code */
include ( get_theme_file_path('/includes/widgets.php') );
add_action("widgets_init", 'ju_widgets');

/theme_dir/includes/widgets.php

function ju_widgets() {
    register_sidebar([
        'name'          => __('My First Theme Sidebar', 'udemy'),
        'id'            => 'ju_sidebar',
        'description'   => __('Sidebar for the theme Udemy', 'udemy'),
        'before_widget' => '<div id="%1$s" class="widget clearfix %2$s">',
        'after_widget'  => '</div>',
        'before_title'  => '<h4>',
        'after_title'   => '</h4>',
    ]);
}

/theme_dir/sidebar.php

<div class="sidebar nobottommargin col_last">
    <div class="sidebar-widgets-wrap">
        <?php
            if (is_active_sidebar('ju_sidebar')) {
                dynamic_sidebar('ju_sidebar');
            }
        ?>
    </div>
</div>

/theme_dir/searchform.php

<?php $unique_id = esc_attr( uniqid( 'search-form-' ) ); ?>

<form role="search" method="get" class="search-form"
      action="<?php echo esc_url( home_url( '/' ) ); ?>">
    <div class="input-group">
        <input type="search" id="<?php echo $unique_id; ?>"
               class="form-control" name="s"
               value="<?php the_search_query(); ?>"
               placeholder="<?php _e( 'Search', 'udemy' ); ?>"/>
        <span class="input-group-btn">
            <button type="submit" class="btn btn-danger"><i class="icon-search"></i></button>
        </span>
    </div>
</form>

/theme_dir/index.php

<!-- some theme html -->

<?php get_sidebar(); ?>

<!-- other theme html -->

No matter what I change in the searchform.php file, it doesn’t replace the default search widget.