How to add opacity in the bootstrap menu

Question

I’m starting now to mess with both site and bootstrap, I’m using wordpress tbm. OK my doubt is the following, I added the standard bootstrap menu on my site, and I left it fixed at the top tbm, I would like to know now how I do to mess with his opacity, so that when I scroll down the site it n get overlapping the content of the site, thus giving to see part of the content even with the fixed menu.

I searched and still did not find, I wonder if it is through the HTML itself that gives to do this, or I will have to do it through css msm...

Menu code.

<nav class="navbar navbar-default">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
        <span class="sr-only">Toggle navigation</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Brand</a>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
        <li class="active"><a href="#">Link <span class="sr-only">(current)</span></a></li>
        <li><a href="#">Link</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
          <ul class="dropdown-menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">Separated link</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">One more separated link</a></li>
          </ul>
        </li>
      </ul>
      <form class="navbar-form navbar-left">
        <div class="form-group">
          <input type="text" class="form-control" placeholder="Search">
        </div>
        <button type="submit" class="btn btn-default">Submit</button>
      </form>
      <ul class="nav navbar-nav navbar-right">
        <li><a href="#">Link</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
          <ul class="dropdown-menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">Separated link</a></li>
          </ul>
        </li>
      </ul>
    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>

Answer 1

If you add opacity in the navbar class it’s not right?

.navbar
{
   opacity: 0.7;
}

The bootstrap itself does not have an opacity helper, do it by CSS itself

EDIT:

For the menu to be opaque only when you scroll down the page, try doing so: Create a class in css:

.opaque
{
   opacity: 0.7;
}

Leave navbar fixed on top:

<nav class="navbar navbar-default navbar-fixed-top">

And use this jQuery, so that when you scroll the page, it adds the Opaque class to the navbar, and when it comes back to the top, it removes:

$(window).scroll(function() {
    if ($(".navbar").offset().top > 50) {
        $(".navbar-fixed-top").addClass("opaque");
    } else {
        $(".navbar-fixed-top").removeClass("opaque");
    }
});