'HTML/CSS -- Making a column with a Left and Right Side for content

I am working on a project to create a webpage. I have been trying to get these two boxes side by side each other. But I am only getting them stacking on top of each other and in the center or left side of the page.

Below is a reproducible example you will be able to see the current code. All I need is the two boxes to be side by side each other with the left and right class that I already have put in. As, i want to use this technique to add more chapters below the first two. Like this;

nav{
    display: flex;
    padding: 2% 6%;
    justify-content: space-between;
    align-items: center;
}
nav img{
    width: 250px;
    height: 70px;
}
.nav-links{
    flex: 1;
    text-align: right;

}
.nav-links ul li{
    list-style:  none;
    display: inline-block;
    padding: 8px 12px;
    position: relative;
}
.nav-links ul li a{
    color: #fff;
    text-decoration: none;
    font-size: 13px;
}
.nav-links ul li::after{
    content: '';
    width: 0%;
    height: 2px;
    background: #f44336;
    display: block;
    margin: auto;
    transition: 0.5s;
}
.nav-links ul li:hover::after{
    width: 100%;
}
.cpp-chapter{
    margin: auto;
    width: 80%;
    padding: 60px 0;
    display: fixed;
}
.cpp-chapter-col{
    width: 80%;
    margin: auto;
    border-radius: 8px;
    padding: 0 11px 9px;
    box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
    max-width: 800px;
    margin-bottom: 12px;
}
.cpp-chapter h1{
    color: #111;
    text-transform: uppercase;
    font-weight: 600;
    text-align: center;
}
.blog-content{
    width: 80%;
    margin: auto;
    padding: 60px 0;
}
.chapter-header{
    padding-bottom: 4px;
}
.chapter-header-num{
    color: #fff;
    font-size: 1.2rem;
    float: right;
    background-color: #f44336;
    padding: 0 8px;
    border-bottom-left-radius: 8px;
    border-bottom-right-radius: 8px;

}
.chapter-header-title{
    color: #3B4C5A;
    font-size: 1.4rem;
    font-weight: 400;
    padding-top: 4px;
}
.cpp-chapter-list{
    margin-top: 4px;
}
.lesson-row{
    margin: 3px 0;
    border-radius: 6px;
    display: flex;
    align-items: center;
    transition: .1s all;
}
.lesson-row-num{
    background: #f44336;
    color: #fff;
    font-size: 1.1rem;
    font-weight: 400;
    border-radius: 4px;
    padding: 0;
    margin: 3px 10px 3px 4px;
    width: 46px;
    min-width: 46px;
    text-align: center;
    line-height: 20px;
}
.chapter-left{
    flex-basis: 50%;
}
.chapter-right{
    flex-basis: 50%;
}
<!DOCTYPE html>

<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>Final Project</title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="../public/css/style.css">

        <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.15.4/css/all.css" integrity="sha384-DyZ88mC6Up2uqS4h/KRgHuoeGwBcD4Ng9SiP4dIRy0EXTlnuz47vAwmeGwVChigm" crossorigin="anonymous">
        <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    </head>
    <body>
        <section class="tut-header">
            <nav>
                <div class="nav-links" id="navLinks">
                    <i class="fas fa-times" onclick="hideMenu()"></i>
                    <ul>
                        <li><a href="index.html">HOME</a></li>
                        <li><a href="about.html">ABOUT</a></li>
                        <li><a href="course.html">COURSE</a></li>
                        <li><a href="getStarted.html">GET STARTED</a></li>
                        <li><a href="blog.html">BLOG</a></li>
                        <li><a href="contact.html">CONTACT</a></li>
                    </ul>
                </div>
                <i class="fas fa-bars" onclick="showMenu()"></i>
            </nav>
        <!-- Chapter Section -->
        <section class="cpp-chapter">
            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-left">                                  <!--Chapter Left Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 1</div>
                        <div class="chapter-header-title">C++ Basics</div>
                    </div>                                                  <!--Chapter Header End -->

                    <div class="cpp-chapter-list">                          <!--Chapter List Start -->

                        <div class="lesson-row">
                            <div class="lesson-row-num">1.1</div>
                            <div class="lesson-row-title">Statements and the Structure of a Program</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">1.2</div>
                            <div class="lesson-row-title">Comments</div>
                        </div>

                    </div>  <!--Chapter List End -->
                </div>  <!--Chapter Left End -->
            </div>  <!--Chapter Column End -->



            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-right">                                 <!--Chapter Right Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 2</div>
                        <div class="chapter-header-title">C++ Basics: Functions and Files</div>
                    </div>                                                  <!--Chapter Header End -->
                    
                    <div class="cpp-chapter-list">                          <!--Chapter List Start-->

                        <div class="lesson-row">
                            <div class="lesson-row-num">2.1</div>
                            <div class="lesson-row-title">Introduction to Functions</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">2.2</div>
                            <div class="lesson-row-title">Return Values</div>
                        </div>

                    </div><!--Chapter List End -->
                </div><!--Chapter Right End -->
            </div><!--Chapter Column End -->
        </section>

     <script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script>
     <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
     <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script>  
    </body>
</html>


Solution 1:[1]

I added

.cpp-chapter-col{
width: 50%;
float: left;

To get the elements to show next to each other

nav{
    display: flex;
    padding: 2% 6%;
    justify-content: space-between;
    align-items: center;
}
nav img{
    width: 250px;
    height: 70px;
}
.nav-links{
    flex: 1;
    text-align: right;

}
.nav-links ul li{
    list-style:  none;
    display: inline-block;
    padding: 8px 12px;
    position: relative;
}
.nav-links ul li a{
    color: #fff;
    text-decoration: none;
    font-size: 13px;
}
.nav-links ul li::after{
    content: '';
    width: 0%;
    height: 2px;
    background: #f44336;
    display: block;
    margin: auto;
    transition: 0.5s;
}
.nav-links ul li:hover::after{
    width: 100%;
}
.cpp-chapter{
    margin: auto;
    width: 80%;
    padding: 60px 0;
    display: fixed;
}
.cpp-chapter-col{
    width: 50%;
    float: left;
    margin: auto;
    border-radius: 8px;
    padding: 0 11px 9px;
    box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
    max-width: 800px;
    margin-bottom: 12px;
}
.cpp-chapter h1{
    color: #111;
    text-transform: uppercase;
    font-weight: 600;
    text-align: center;
}
.blog-content{
    width: 80%;
    margin: auto;
    padding: 60px 0;
}
.chapter-header{
    padding-bottom: 4px;
}
.chapter-header-num{
    color: #fff;
    font-size: 1.2rem;
    float: right;
    background-color: #f44336;
    padding: 0 8px;
    border-bottom-left-radius: 8px;
    border-bottom-right-radius: 8px;

}
.chapter-header-title{
    color: #3B4C5A;
    font-size: 1.4rem;
    font-weight: 400;
    padding-top: 4px;
}
.cpp-chapter-list{
    margin-top: 4px;
}
.lesson-row{
    margin: 3px 0;
    border-radius: 6px;
    display: flex;
    align-items: center;
    transition: .1s all;
}
.lesson-row-num{
    background: #f44336;
    color: #fff;
    font-size: 1.1rem;
    font-weight: 400;
    border-radius: 4px;
    padding: 0;
    margin: 3px 10px 3px 4px;
    width: 46px;
    min-width: 46px;
    text-align: center;
    line-height: 20px;
}
.chapter-left{
    flex-basis: 50%;
}
.chapter-right{
    flex-basis: 50%;
}
<!DOCTYPE html>

<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>Final Project</title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="../public/css/style.css">

        <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.15.4/css/all.css" integrity="sha384-DyZ88mC6Up2uqS4h/KRgHuoeGwBcD4Ng9SiP4dIRy0EXTlnuz47vAwmeGwVChigm" crossorigin="anonymous">
        <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    </head>
    <body>
        <section class="tut-header">
            <nav>
                <div class="nav-links" id="navLinks">
                    <i class="fas fa-times" onclick="hideMenu()"></i>
                    <ul>
                        <li><a href="index.html">HOME</a></li>
                        <li><a href="about.html">ABOUT</a></li>
                        <li><a href="course.html">COURSE</a></li>
                        <li><a href="getStarted.html">GET STARTED</a></li>
                        <li><a href="blog.html">BLOG</a></li>
                        <li><a href="contact.html">CONTACT</a></li>
                    </ul>
                </div>
                <i class="fas fa-bars" onclick="showMenu()"></i>
            </nav>
        <!-- Chapter Section -->
        <section class="cpp-chapter">
            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-left">                                  <!--Chapter Left Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 1</div>
                        <div class="chapter-header-title">C++ Basics</div>
                    </div>                                                  <!--Chapter Header End -->

                    <div class="cpp-chapter-list">                          <!--Chapter List Start -->

                        <div class="lesson-row">
                            <div class="lesson-row-num">1.1</div>
                            <div class="lesson-row-title">Statements and the Structure of a Program</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">1.2</div>
                            <div class="lesson-row-title">Comments</div>
                        </div>

                    </div>  <!--Chapter List End -->
                </div>  <!--Chapter Left End -->
            </div>  <!--Chapter Column End -->



            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-right">                                 <!--Chapter Right Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 2</div>
                        <div class="chapter-header-title">C++ Basics: Functions and Files</div>
                    </div>                                                  <!--Chapter Header End -->
                    
                    <div class="cpp-chapter-list">                          <!--Chapter List Start-->

                        <div class="lesson-row">
                            <div class="lesson-row-num">2.1</div>
                            <div class="lesson-row-title">Introduction to Functions</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">2.2</div>
                            <div class="lesson-row-title">Return Values</div>
                        </div>

                    </div><!--Chapter List End -->
                </div><!--Chapter Right End -->
            </div><!--Chapter Column End -->
        </section>

     <script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script>
     <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
     <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script>  
    </body>
</html>

Solution 2:[2]

         nav{
        display: flex;
        padding: 2% 6%;
        justify-content: space-between;
        align-items: center;
    }
    nav img{
        width: 250px;
        height: 70px;
    }
    .nav-links{
        flex: 1;
        text-align: right;
    
    }
    .nav-links ul li{
        list-style:  none;
        display: inline-block;
        padding: 8px 12px;
        position: relative;
    }
    .nav-links ul li a{
        color: #fff;
        text-decoration: none;
        font-size: 13px;
    }
    .nav-links ul li::after{
        content: '';
        width: 0%;
        height: 2px;
        background: #f44336;
        display: block;
        margin: auto;
        transition: 0.5s;
    }
    .nav-links ul li:hover::after{
        width: 100%;
    }
    .cpp-chapter{
        margin: auto;
        width: 80%;
        padding: 60px 0;
        display: fixed;
    }
    .cpp-chapter-col{
        width: 50%;
        float:left;
        margin: auto;
        border-radius: 8px;
        padding: 0 11px 9px;
        box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
        max-width: 800px;
        margin-bottom: 12px;
    }
    .cpp-chapter h1{
        color: #111;
        text-transform: uppercase;
        font-weight: 600;
        text-align: center;
    }
    .blog-content{
        width: 80%;
        margin: auto;
        padding: 60px 0;
    }
    .chapter-header{
        padding-bottom: 4px;
    }
    .chapter-header-num{
        color: #fff;
        font-size: 1.2rem;
        float: right;
        background-color: #f44336;
        padding: 0 8px;
        border-bottom-left-radius: 8px;
        border-bottom-right-radius: 8px;
    
    }
    .chapter-header-title{
        color: #3B4C5A;
        font-size: 1.4rem;
        font-weight: 400;
        padding-top: 4px;
    }
    .cpp-chapter-list{
        margin-top: 4px;
    }
    .lesson-row{
        margin: 3px 0;
        border-radius: 6px;
        display: flex;
        align-items: center;
        transition: .1s all;
    }
    .lesson-row-num{
        background: #f44336;
        color: #fff;
        font-size: 1.1rem;
        font-weight: 400;
        border-radius: 4px;
        padding: 0;
        margin: 3px 10px 3px 4px;
        width: 46px;
        min-width: 46px;
        text-align: center;
        line-height: 20px;
    }
    .chapter-left{
        flex-basis: 50%;
    }
    .chapter-right{
        flex-basis: 50%;
    }

    <!DOCTYPE html>

<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>Final Project</title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="../public/css/style.css">

        <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.15.4/css/all.css" integrity="sha384-DyZ88mC6Up2uqS4h/KRgHuoeGwBcD4Ng9SiP4dIRy0EXTlnuz47vAwmeGwVChigm" crossorigin="anonymous">
        <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    </head>
    <body>
        <section class="tut-header">
            <nav>
                <div class="nav-links" id="navLinks">
                    <i class="fas fa-times" onclick="hideMenu()"></i>
                    <ul>
                        <li><a href="index.html">HOME</a></li>
                        <li><a href="about.html">ABOUT</a></li>
                        <li><a href="course.html">COURSE</a></li>
                        <li><a href="getStarted.html">GET STARTED</a></li>
                        <li><a href="blog.html">BLOG</a></li>
                        <li><a href="contact.html">CONTACT</a></li>
                    </ul>
                </div>
                <i class="fas fa-bars" onclick="showMenu()"></i>
            </nav>
        <!-- Chapter Section -->
        <section class="cpp-chapter">
            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-left">                                  <!--Chapter Left Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 1</div>
                        <div class="chapter-header-title">C++ Basics</div>
                    </div>                                                  <!--Chapter Header End -->

                    <div class="cpp-chapter-list">                          <!--Chapter List Start -->

                        <div class="lesson-row">
                            <div class="lesson-row-num">1.1</div>
                            <div class="lesson-row-title">Statements and the Structure of a Program</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">1.2</div>
                            <div class="lesson-row-title">Comments</div>
                        </div>

                    </div>  <!--Chapter List End -->
                </div>  <!--Chapter Left End -->
            </div>  <!--Chapter Column End -->



            <div class="cpp-chapter-col">                                   <!--Chapter Column Start -->
                <div class="chapter-right">                                 <!--Chapter Right Start -->

                    <div class="chapter-header">                            <!--Chapter Header Start -->
                        <a name="Chapter1"></a>
                        <div class="chapter-header-num">Chapter 2</div>
                        <div class="chapter-header-title">C++ Basics: Functions and Files</div>
                    </div>                                                  <!--Chapter Header End -->
                    
                    <div class="cpp-chapter-list">                          <!--Chapter List Start-->

                        <div class="lesson-row">
                            <div class="lesson-row-num">2.1</div>
                            <div class="lesson-row-title">Introduction to Functions</div>
                        </div>
                        <div class="lesson-row">
                            <div class="lesson-row-num">2.2</div>
                            <div class="lesson-row-title">Return Values</div>
                        </div>

                    </div><!--Chapter List End -->
                </div><!--Chapter Right End -->
            </div><!--Chapter Column End -->
        </section>

     <script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script>
     <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
     <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script>  
    </body>
</html>

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 BCT
Solution 2