Making navbar transparent and putting the image behind

I am making a website and I am using Bootstrap for this. I just want to make the navbar transparent and Put the image behind it.

My HTML code for Navbar is:

    <pre lang="HTML"><nav class="navbar navbar-expand-lg navbar-light">
      <a class="navbar-brand" href="#">LOTL</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 ml-auto">
          <li class="nav-item active">
            <a class="nav-link" href="#">Home</a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">About</a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">Join</a>
          </li>
        </ul>
      </div>
    </nav>

<img class="first-wallpaper" src="Images/League First Page.jpg" alt="legaue-wallpaper">