Bootstrap affix - Cant manage to hide image element when scrolling down

Question

When I scroll down I want to hide the big logo and expose the small logo

<div class="row clearfix" >
  <div class="col-md-12 column">
    <nav class="navbar navbar-default" role="navigation" data-spy="affix" data-offset-top="10">
      <div class="navbar-header"> <a class="big_logo" href="#"><img src="img/logo.png" alt="logo"></a><a class="small_logo" href="#"><img src="img/logo_small.png" alt="logo_small"></a></div>
    </nav>
  </div>
</div>

I dont know what I am messing up here in my CSS:

.big_logo {
}
.big_logo.affix {
        display:none;
}
.small_logo {
        display:none;
}
.small_logo.affix {
}

Answer 1

You are expecting .big_logo and .small_logo to get the class .affix. It's the element that has data-spy="affix" that's actually getting the .affix class so you need to modify your CSS selector to .affix .big_logo instead of .big_logo.affix like this:

.small_logo {
    display: none;
}
.affix .small_logo {
    display: block;
}
.affix .big_logo {
    display: none;
}