Fixed sidebar – no CSS knowledge

Hi there! I’ve searched the forums and been unable to find an answer to this question that I can implement successfully… I’m trying to create a fixed sidebar that will remain in place while content scrolls. I have zero CSS knowledge (though I do have some 15-year-old html knowledge), so a lot of what I’ve looked at here is really hard for me to understand.

My website is https://www.jenniesteinberg.com

I see two files that look like they might be my sidebar. One is sidebar-default.php and looks like this:

<?php
/**
 * Template part file for default sidebar.
 *
 *
 * @package Raindrops
 * @since Raindrops 0.1
 */
?>
<div class="lsidebar">
<ul>
<?php
	if (!dynamic_sidebar('sidebar-1')){
		raindrops_sidebar_menus( 'default' );
	}
?>
</ul>
</div>

And the other is just called “Sidebar” and then says “sidebar.php” in parentheses. That code looks like this:

<?php
/**
* Template part file for Sidebar.
*
*
* @package Raindrops
*/
?>
<div class="sidebar">
<ul>
<?php if (!dynamic_sidebar('sidebar-1')){ ?>
<?php wp_list_pages('title_li=<h2 class="h2">'. __( 'Pages', 'Raindrops').'</h2>' ); ?>
<li><h2 class="h2"><?php _e( 'Archives', 'Raindrops' ); ?></h2>
  <ul>
    <?php wp_get_archives('type=monthly'); ?>
  </ul>
</li>
<?php wp_list_categories('show_count=1&title_li=<h2 class="h2">'. __( 'Categories', 'Raindrops'). '</h2>'); ?>
<?php /* If this is the frontpage */ if ( is_front_page() || is_page() ) { ?>
<?php wp_list_bookmarks(); ?>
<li>
  <h2 class="h2">Meta<?php _e( 'Meta', 'Raindrops' ); ?></h2>
  <ul>
    <?php wp_register(); ?>
    <li>
      <?php wp_loginout(); ?>
    </li>
    <?php wp_meta(); ?>
  </ul>
</li>
<?php } ?>
<?php } ?>
</ul>
</div>

I am using Raindrops theme.

Which of these files do I need to modify in order to have the sidebar be fixed while website visitors scroll through text?

Thanks,

Jennie