Bootstrap 4 multiple fixed Navbars with animated shrink

Question

I have two Navbars with fixed-top classes displayed one below the other - second one having top: *height of first navbar* css added to it.

Answer 1

I think you should wrap both navbars in a single DIV, and make that the data-toggle="affix" element. This way you only make the outer DIV fixed, and the second navbar will naturally follow the height of the 2nd since both are static position.

https://www.codeply.com/go/DpHESPqZsx

<div class="fixed-top" data-toggle="affix">
    <div class="navbar navbar-dark bg-dark navbar-expand-sm py-5" id="first">
        ... 
    </div>
    <div class="navbar navbar-light bg-light navbar-expand-sm" id="second">
        ...
    </div>
</div>

Adjust the CSS to apply the padding animation to the top navbar instead of the affix element:

.fixed-top #first { 
  -webkit-transition:padding 0.2s ease;
  -moz-transition:padding 0.2s ease; 
  -o-transition:padding 0.2s ease;        
  transition:padding 0.2s ease;  
}

.affix #first {
  padding-top: 0.2em !important;
  padding-bottom: 0.2em !important;
  -webkit-transition:padding 0.2s linear;
  -moz-transition:padding 0.2s linear;  
  -o-transition:padding 0.2s linear;         
  transition:padding 0.2s linear;  
}