bootstrap landing pages greyscale code example

Example: how to create a large rectangle on landing page using bootstrap

<!-- navbar -->  
 <nav class="navbar navbar-expand-lg fixed-top ">  
 <a class="navbar-brand" href="#">Home</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">  
 <span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse " id="navbarSupportedContent">     <ul class="navbar-nav mr-4">
 <li class="nav-item">
     <a class="nav-link" data-value="about" href="#">About</a>        </li>  
<li class="nav-item">
    <a class="nav-link " data-value="portfolio"href="#">Portfolio</a>    
 </li>
 <li class="nav-item"> 
    <a class="nav-link " data-value="blog" href="#">Blog</a>         </li>   
<li class="nav-item">  
   <a class="nav-link " data-value="team" href="#">         Team</a>       </li>  
<li class="nav-item"> 
 <a class="nav-link " data-value="contact" href="#">Contact</a>       </li> 
</ul> 
</div></nav>