Página de documentación técnica - Construye una Página de Documentación Técnica

Cuéntanos qué está pasando:

Hola.
No me aprueba el paso 19 y 20 y no encuentro el error.

<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Music</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="stylesheet" href="./styles.css">
  </head>
  <body>
    <h1>Music</h1>
    <main id="main-doc">
      <section id="Lets_Start" class="main-section">
        <header>Lets Start</header>
            <nav id="navbar">      
              <header>Info Box</header>     
            <ul>  
              <li><a class="nav-link" href="#Introduction">Introduction</a></li>
              <li><a class="nav-link" href="#What_you_should_already_know">What you should already know</a></li>
              <li><a class="nav-link" href="#Guitar">Guitar</a></li>
              <li><a class="nav-link" href="#Bass">Bass</a></li>
              <li><a class="nav-link" href="#Drums">Drums</a></li>
              <li><a class="nav-link" href="#Piano">Piano</a></li>
              <li><a class="nav-link" href="#Sing">Sing</a></li>
              <li><a class="nav-link" href="#Lessons">Lessons</a></li>
              <li><a class="nav-link" href="#Instruments_Price">Instruments Price</a></li>
              <li><a class="nav-link" href="#Music_Lifestyle">Music Lifestyle</a></li>  
            </nav>
            
            <section id="Introduction">
            <header>Introduction</header>
        <code>
        <p>If you want to keep your brain engaged throughout the aging process, listening to or playing music is a great tool. It provides a total brain workout. Research has shown that listening to music can reduce anxiety, blood pressure, and pain as well as improve sleep quality, mood, mental alertness, and memory.</p>
        </code>
      </section>
      <section id="What_you_should_already_know" class="main-section">
        <header>What you should already know</header>
        <code>
        <p>Engaging with music stimulates the brain, triggering the release of dopamine, the 'feel-good' chemical, promoting relaxation and uplifted mood. Additionally, it offers a form of self-expression, allowing individuals to process emotions they might find challenging to articulate</p>
        </code>
      </section>
      <section id="Guitar" class="main-section">
        <header>Guitar</header>
        <code>
        <p>For starters, it is a great way to relieve stress. It can also help you connect with other people who share your passion for music. Playing guitar can also improve your coordination and fine motor skills. In addition, research has shown that playing guitar can improve your memory and cognitive skills.</p>
        </code>
      </section>
      <section id="Bass" class="main-section">
        <header>Bass</header>
        <code>
        <p>The lower frequencies, it seems, strong-arm the brain into synchronizing. This helps explain why a bass-heavy sound might make people more inclined to move along: the lower frequencies, as the authors write, boost “selective neural locking to the beat.”</p>
        </code>
      </section>
      <section id="Drums" class="main-section">
        <header>Drums</header>
        <code>
        <p>According to researchers, drumming can not only alter your mood, but it reduces stress, lowers blood pressure and even enhances your immunity. There's also evidence that drumming releases endorphins, enkephalins and Alpha waves in the brain, which are associated with general feelings of well-being and euphoria.</p>
        </code>
      </section>
      <section id="Piano" class="main-section">
        <header>Piano</header>
        <code>
        <p>Studies show that time spent at the keyboard improves mental health: people who make music experience less anxiety, loneliness, and depression. Playing piano has also been shown to be a great source of stress relief, and provides ample opportunities to bolster self-esteem.</p>
        </code>
        </section>
        <section id="Sing" class="main-section">
        <header>Sing</header>
        <code>
        <p>Singing releases endorphins, the feel-good chemicals in the brain. Singing also promotes deep breathing, as you need to take deep breaths and control your breathing. In fact, singing is an aerobic activity, which means it gets oxygen into your blood, improving circulation and it boosts your mood.</p>
        </code>
        <section id="Lessons" class="main-section">
        <header>Lessons</header>
        <code>
        <p>On average, private music lessons can range from $30 to $100 per hour, with most falling in the $50 to $75 range. However, it is essential to consider more than just the monetary cost when assessing the value of music education.</p>
        </code>
         <section id="Instruments_Price" class="main-section">
        <header>Instruments Price</header>
        <code>
        <p>The average price of a stringed school instrument in the U.S. experienced a generally increasing trend from 2005 to 2021. In 2021, the average price for a stringed school instrument was 400 U.S. dollars, 30 U.S. dollars more than in the previous year.</p>
        <ul>
          <li>Guitar $100-$300</li>
          <li>Bass $100-$300</li>
          <li>Piano $100-$500</li>
          <li>Drums $200-$600</li>
          <li>Microphone $100-$300</li>
        </ul>
        </code>
    <section id="Music_Lifestyle" class="main-section">
        <header>Music Lifestyle</header>
        <code>
        <p>Yes, it's absolutely possible to make a living as a musician. However, it requires dedication, creativity, and consistent effort. While it may seem like a trendy pursuit, many individuals have built successful careers in these fields through passion, hard work, and strategic planning.</p>
        </code>
     </section>
     </main>
    </body>

Cuando pidas ayuda, por favor proporciona el enlace al proyecto.

Este es el enlace al proyecto:

this should not be .main-section
or if you want it to be, it needs to have a corresponding .nav-link

Thx!..