I have a problem with User Story #10: Additionally, the navbar should contain link (a) elements with the class of nav-link. so can you any help me and thank you

 <nav id="navbar">
    <header>JS Documentation</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="#JavaScript_and_Java">JavaScript and Java</a></li>
      <li> <a class="nav-link" href="#Hello_world">Hello world</a></li>
      <li> <a class="nav-link" href="#Variables">Variables</a></li>
      <li> <a class="nav-link" href="#Declaring_variables">Declaring variables</a></li>
      <li> <a class="nav-link" href="#Variable_scope">Variable scope</a></li>
      <li> <a class="nav-link" href="#Global_variables">Global variables</a></li>
      <li> <a class="nav-link" href="#Constants">Constants</a></li>
      <li> <a class="nav-link" href="#Data_types">Data types</a></li>
      <li> <a class="nav-link" href="#if...else_statement">if...else statement</a></li>
      <li> <a class="nav-link" href="#while_statement">while statement</a></li>
      <li> <a class="nav-link" href="#Function_declarations">Function declarations</a></li>
      <li> <a class="nav-link" href="#Reference">Reference</a></li>
    </ul>
  </nav>
  <main id="main-doc">
    <section id="Introduction" class="main-section">
      <header>Introduction</header>
      <article>
        <p>JavaScript is a cross-platform, object-oriented scripting language. It is a small and lightweight language.
          Inside a
          host environment (for example, a web browser), JavaScript can be connected to the objects of its environment
          to
          provide
          programmatic control over them.</p>

        <p>JavaScript contains a standard library of objects, such as Array, Date, and Math, and a core set of language
          elements
          such as operators, control structures, and statements. Core JavaScript can be extended for a variety of
          purposes
          by
          supplementing it with additional objects; for example:</p>
        <ul>
          <li>Client-side JavaScript extends the core language by supplying objects to control a browser and its
            Document
            Object Model
            (DOM). For example, client-side extensions allow an application to place elements on an HTML form and
            respond
            to user
            events such as mouse clicks, form input, and page navigation.</li>
          <li>Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a
            server. For
            example, server-side extensions allow an application to communicate with a database, provide continuity of
            information
            from one invocation to another of the application, or perform file manipulations on a server.</li>
        </ul>
      </article>
    </section>
    <section id="What_you_should_already_know" class="main-section">
      <header>What you should already know</header>
      <article>
        <p>This guide assumes you have the following basic background:</p>
        <ul>
          <li>A general understanding of the Internet and the World Wide Web (WWW).
          </li>
          <li>Good working knowledge of HyperText Markup Language (HTML).
          </li>
          <li>Some programming experience. If you are new to programming, try one of the tutorials linked on the main
            page
            about
            JavaScript.
          </li>
        </ul>
      </article>
    </section>
    <section id="JavaScript_and_Java" class="main-section">
      <header>JavaScript and Java</header>
      <p>JavaScript and Java are similar in some ways but fundamentally different in some others. The JavaScript
        language
        resembles Java but does not have Java's static typing and strong type checking. JavaScript follows most Java
        expression
        syntax, naming conventions and basic control-flow constructs which was the reason why it was renamed from
        LiveScript to
        JavaScript.</p>
      <p>In contrast to Java's compile-time system of classes built by declarations, JavaScript supports a runtime
        system based
        on a small number of data types representing numeric, Boolean, and string values. JavaScript has a
        prototype-based
        object model instead of the more common class-based object model. The prototype-based model provides dynamic
        inheritance; that is, what is inherited can vary for individual objects. JavaScript also supports functions
        without any
        special declarative requirements. Functions can be properties of objects, executing as loosely typed methods.
      </p>
      <p>JavaScript is a very free-form language compared to Java. You do not have to declare all variables, classes,
        and
        methods. You do not have to be concerned with whether methods are public, private, or protected, and you do not
        have to
        implement interfaces. Variables, parameters, and function return types are not explicitly typed.
      </p>
    </section>
    <section id="Hello_world" class="main-section">
      <header>Hello world</header>
      <p>To get started with writing JavaScript, open the Scratchpad and write your first "Hello world" JavaScript code:
      </p>
      <code>function greetMe(yourName) { alert("Hello " + yourName); }
        greetMe("World");</code>
      <p>Select the code in the pad and hit Ctrl+R to watch it unfold in your browser!</p>
    </section>
    <section id="Variables" class="main-section">
      <header>Variables</header>
      <p>You use variables as symbolic names for values in your application. The names of variables, called identifiers,
        conform
        to certain rules.</p>
      <p>A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($); subsequent characters can
        also be
        digits (0-9). Because JavaScript is case sensitive, letters include the characters "A" through "Z" (uppercase)
        and the
        characters "a" through "z" (lowercase).
      </p>
      <p>You can use ISO 8859-1 or Unicode letters such as å and ü in identifiers. You can also use the Unicode escape
        sequences
        as characters in identifiers. Some examples of legal names are Number_hits, temp99, and _name.
      </p>
    </section>
    <section id="Declaring_variables" class="main-section">
      <header>Declaring variables</header>
      <p>You can declare a variable in three ways:</p>
      <p>With the keyword var. For example,</p>
      <code>var x = 42.</code>
      <p>This syntax can be used to declare both local and global variables.</p>
      <p>By simply assigning it a value. For example,</p>
      <code>x = 42.</code>
      <p>This always declares a global variable. It generates a strict JavaScript warning. You shouldn't use this
        variant.
      </p>
      <p>With the keyword let. For example,
      </p>
      <code>let y = 13.</code>
      <p>This syntax can be used to declare a block scope local variable. See Variable scope below.
      </p>
    </section>
    <section id="Variable_scope" class="main-section">
      <header>Variable scope</header>
      <p>When you declare a variable outside of any function, it is called a global variable, because it is available to
        any
        other code in the current document. When you declare a variable within a function, it is called a local
        variable,
        because it is available only within that function.
      </p>
      <p>JavaScript before ECMAScript 2015 does not have block statement scope; rather, a variable declared within a
        block is
        local to the function (or global scope) that the block resides within. For example the following code will log
        5,
        because the scope of x is the function (or global context) within which x is declared, not the block, which in
        this case
        is an if statement.
      </p>
      <code>if (true) { var x = 5; } console.log(x); // 5</code>
      <p>This behavior changes, when using the let declaration introduced in ECMAScript 2015.
      </p>
      <code>if (true) { let y = 5; } console.log(y); // ReferenceError: y is not
        defined</code>
    </section>
    <section id="Global_variables" class="main-section">
      <header>Global variables</header>
      <p>Global variables are in fact properties of the global object. In web pages the global object is window, so you
        can set
        and access global variables using the window.variable syntax.
      </p>
      <p>Consequently, you can access global variables declared in one window or frame from another window or frame by
        specifying
        the window or frame name. For example, if a variable called phoneNumber is declared in a document, you can refer
        to this
        variable from an iframe as parent.phoneNumber.
      </p>
    </section>
    <section id="Constants" class="main-section">
      <header>Constants</header>
      <p>You can create a read-only, named constant with the const keyword. The syntax of a constant identifier is the
        same as
        for a variable identifier: it must start with a letter, underscore or dollar sign and can contain alphabetic,
        numeric,
        or underscore characters.</p>
      <code>const PI = 3.14;</code>
      <p>A constant cannot change value through assignment or be re-declared while the script is running. It has to be
        initialized to a value.
      </p>
      <p>The scope rules for constants are the same as those for let block scope variables. If the const keyword is
        omitted, the
        identifier is assumed to represent a variable.</p>
      <p>You cannot declare a constant with the same name as a function or variable in the same scope. For example:
      </p>
      <code>// THIS WILL CAUSE AN ERROR function f() {}; const f = 5; // THIS WILL
              CAUSE AN ERROR ALSO function f() { const g = 5; var g; //statements}</code>
      <p>However, object attributes are not protected, so the following statement is executed without problems.
      </p>
      <code>const MY_OBJECT = {"key": "value"}; MY_OBJECT.key = "otherValue";</code>
    </section>
    <section id="Data_types" class="main-section">
      <header>Data types</header>
      <p>Data types</p>
      <ul>
        <li>Six data types that are primitives:</li>
        <ul>
          <li>Boolean. true and false.</li>
          <li>null. A special keyword denoting a null value. Because JavaScript is case-sensitive, null is not the same
            as Null, NULL,
            or any other variant.
          </li>
          <li>undefined. A top-level property whose value is undefined.</li>
          <li>Number. 42 or 3.14159.</li>
          <li>String. "Howdy"</li>
          <li>Symbol (new in ECMAScript 2015). A data type whose instances are unique and immutable.
          </li>
        </ul>
        <li>and Object</li>
      </ul>
      <p>Although these data types are a relatively small amount, they enable you to perform useful functions with your
        applications. Objects and functions are the other fundamental elements in the language. You can think of objects
        as
        named containers for values, and functions as procedures that your application can perform.
      </p>
    </section>
    <section id="if...else_statement" class="main-section">
      <header>if...else statement</header>
      <p>Use the if statement to execute a statement if a logical condition is true. Use the optional else clause to
        execute a
        statement if the condition is false. An if statement looks as follows:
      </p>
      <code>if (condition) { statement_1; } else { statement_2; }</code>
      <p>condition can be any expression that evaluates to true or false. See Boolean for an explanation of what
        evaluates to
        true and false. If condition evaluates to true, statement_1 is executed; otherwise, statement_2 is executed.
        statement_1
        and statement_2 can be any statement, including further nested if statements.
      </p>
      <p>You may also compound the statements using else if to have multiple conditions tested in sequence, as follows:
      </p>
      <code>if (condition_1) { statement_1; } else if (condition_2) { statement_2;
        } else if (condition_n) { statement_n; } else { statement_last; }</code>
      <p>In the case of multiple conditions only the first logical condition which evaluates to true will be executed.
        To execute
        multiple statements, group them within a block statement ({ ... }) . In general, it's good practice to always
        use block
        statements, especially when nesting if statements:
      </p>
      <code>if (condition) { statement_1_runs_if_condition_is_true;
          statement_2_runs_if_condition_is_true; } else {
          statement_3_runs_if_condition_is_false;
          statement_4_runs_if_condition_is_false; }</code>
      <p>It is advisable to not use simple assignments in a conditional expression, because the assignment can be
        confused with
        equality when glancing over the code. For example, do not use the following code:
      </p>
      <code>if (x = y) { /* statements here */ }</code>
      <p>If you need to use an assignment in a conditional expression, a common practice is to put additional
        parentheses around
        the assignment. For example:
      </p>
      <code>if ((x = y)) { /* statements here */ }</code>
    </section>
    <section id="while_statement" class="main-section">
      <header>while statement</header>
      <p>A while statement executes its statements as long as a specified condition evaluates to true. A while statement
        looks as follows:
      </p>
      <p>while (condition) statement</p>
      <p>If the condition becomes false, statement within the loop stops executing and control passes to the statement
        following the loop.
      </p>
      <p>The condition test occurs before statement in the loop is executed. If the condition returns true, statement is
        executed
        and the condition is tested again. If the condition returns false, execution stops and control is passed to the
        statement following while.
      </p>
      <p>To execute multiple statements, use a block statement ({ ... }) to group those statements.
      </p>
      <p>Example</p>
      <p>The following while loop iterates as long as n is less than three:</p>
      <code>var n = 0; var x = 0; while (n < 3) { n++; x +=n; }</code>
      <p>With each iteration, the loop increments n and adds that value to x. Therefore, x and n take on the following
        values:
      </p>
      <ul>
        <li>After the first pass: n = 1 and x = 1</li>
        <li>After the second pass: n = 2 and x = 3</li>
        <li>After the third pass: n = 3 and x = 6</li>
      </ul>
      <p>After completing the third pass, the condition n < 3 is no longer true, so the loop terminates.</p>
    </section>
    </section>
    <section id="Function_declarations" class="main-section">
      <header>Function declarations</header>
      <p>A function definition (also called a function declaration, or function statement) consists of the function
        keyword, ollowed by:
      </p>
      <ul>
        <li>The name of the function.</li>
        <li>A list of arguments to the function, enclosed in parentheses and separated by commas.</li>
        <li>The JavaScript statements that define the function, enclosed in curly brackets, { }.</li>
      </ul>
      <p>For example, the following code defines a simple function named square:</p>
      <code>function square(number) { return number * number; }</code>
      <p>The function square takes one argument, called number. The function consists of one statement that says to
        return the
        argument of the function (that is, number) multiplied by itself. The return statement specifies the value
        returned by the function.
      </p>
      <code>return number * number;</code>
      <p>Primitive parameters (such as a number) are passed to functions by value; the value is passed to the function,
        but if
        the function changes the value of the parameter, this change is not reflected globally or in the calling
        function.
      </p>
    </section>
    </section>
    <section id="Reference" class="main-section">
      <header>Reference</header>
      <ul>
        <li>All the documentation in this page is taken from <a class="nav-link" id="mdn"
            href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide">MDN</a>
        </li>
      </ul>
    </section>
  </main>

Hello there @AhmedTakeshy , welcome to the forum. Do you have a link to you pen. That way we can try to help you much better.

You should not use <header> like you do:

<header>JS Documentation</header>
<header>Introduction</header>

Only use <header> for the content of the header: which normally contains nav links, logos and other introductory things.

For text headings use the h1-h6 tags.

This is the link for my pen, and thank you