Надеюсь, вы пытаетесь достичь следующего.
/*the sidebar back button*/
/* Style the links inside the sidenav */
#mySidenav a {
position: absolute;
/* Position them relative to the browser window */
left: -80px;
/* Position them outside of the screen */
transition: 0.3s;
/* Adds transition on hover */
padding: 15px;
/* 15px padding */
width: 100px;
/* Sets a specific width */
text-decoration: none;
/* Remove underline */
font-size: 20px;
/* Increase font size */
color: white;
/* White text color */
border-radius: 0 5px 5px 0;
/* Rounded corners on the top right and bottom right side */
}
#mySidenav a:hover {
left: 0;
/* On mouse-over, make the elements appear as they should */
}
/* The about link: 20px from the top with a green background */
#about {
top: 20px;
background-color: #42beb8;
}
/*The Footer*/
#footer {
background-color: rgba(59, 195, 154, 0.87);
width: 100%;
height: 95px;
border-radius: 0px;
padding-top: 5px;
position: relative;
bottom: 0;
margin-top: 20%;
}
/* footer div links settings*/
.footer a:hover {
background-color: rgb(230, 182, 64);
color: black;
}
#footer div {
display: block;
float: right;
width: 20%;
}
/* footer links margins settings */
#footer div h5,
h2 {
margin-bottom: 0;
margin-top: 0;
text-decoration: none;
}
/* horizontal line below footer div */
hr {
width: 85%;
margin-left: 8%;
margin-right: 20%;
height: 1px;
background-color: black;
opacity: 1;
margin-top: 3%;
margin-bottom: auto;
}
/* Main Section */
.main {
display: flex;
justify-content: space-between;
align-items: center;
}
.pic-container {
background-color: grey;
width: 45%;
height: 80%;
}
.pic {
width: 100%;
height: 200px;
background-image: url("https://images.pexels.com/photos/3841338/pexels-photo-3841338.jpeg");
}
<!--sidenav-->
<div id="mySidenav" class="sidenav">
<a href="#" id="about">Back</a>
</div>
<!--Main Section-->
<div class="main">
<div class="pic-container">
<div class="pic pic1">
</div>
<p class="description">This is a description</p>
</div>
<div class="pic-container">
<div class="pic pic2">
</div>
<p class="description">This is a description</p>
</div>
</div>
<!--The footer section-->
<footer class="footer">
<div class="row">
<div id="footer">
<br>
<div align="left">
<h5><a href="social.html">Social Media</a></h5>
</div>
<div align="left">
<h5><a href="mainpage.html">Home</a></h5>
</div>
<div align="center">
<h2> <a href="mainpage.html">Buystuff</a>
<h2>
</div>
<div align="right">
<h5><a href="games.html">Games</a></h5>
</div>
<div align="right">
<h5> <a href="products.html">Products</a></h5>
</div>
<hr>
</div>
</div>
</footer>