Hi,

Personally I think it is better if you don't edit the MDB or Bootstrap stylesheets.

You could add this code into your custom style sheet to overwrite the mdb styles:

.navbar-expand-lg {
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-flow: row nowrap;
    flex-flow: row nowrap;
    -webkit-box-pack: start;
    -ms-flex-pack: start;
    justify-content: flex-start;
  }
  .navbar-expand-lg .navbar-nav {
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-direction: row;
    flex-direction: row;
  }
  .navbar-expand-lg .navbar-nav .dropdown-menu {
    position: absolute;
  }
  .navbar-expand-lg .navbar-nav .dropdown-menu-right {
    right: 0;
    left: auto;
  }
  .navbar-expand-lg .navbar-nav .nav-link {
    padding-right: 0.5rem;
    padding-left: 0.5rem;
  }
  .navbar-expand-lg > .container,
  .navbar-expand-lg > .container-fluid {
    -ms-flex-wrap: nowrap;
    flex-wrap: nowrap;
  }
  .navbar-expand-lg .navbar-collapse {
    display: -webkit-box !important;
    display: -ms-flexbox !important;
    display: flex !important;
    -ms-flex-preferred-size: auto;
    flex-basis: auto;
  }
  .navbar-expand-lg .navbar-toggler {
    display: none;
  }
  .navbar-expand-lg .dropup .dropdown-menu {
    top: auto;
    bottom: 100%;
  }

Take note that you should replace the .navbar-expand-lg class with your nav class.

In the same example (as above) you could edit the bootstrap.css stylesheet. Look for this code:

@media (min-width: 992px) {
  .navbar-expand-lg {
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-flow: row nowrap;
    flex-flow: row nowrap;
    -webkit-box-pack: start;
    -ms-flex-pack: start;
    justify-content: flex-start;
  }
  .navbar-expand-lg .navbar-nav {
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-direction: row;
    flex-direction: row;
  }
  .navbar-expand-lg .navbar-nav .dropdown-menu {
    position: absolute;
  }
  .navbar-expand-lg .navbar-nav .dropdown-menu-right {
    right: 0;
    left: auto;
  }
  .navbar-expand-lg .navbar-nav .nav-link {
    padding-right: 0.5rem;
    padding-left: 0.5rem;
  }
  .navbar-expand-lg > .container,
  .navbar-expand-lg > .container-fluid {
    -ms-flex-wrap: nowrap;
    flex-wrap: nowrap;
  }
  .navbar-expand-lg .navbar-collapse {
    display: -webkit-box !important;
    display: -ms-flexbox !important;
    display: flex !important;
    -ms-flex-preferred-size: auto;
    flex-basis: auto;
  }
  .navbar-expand-lg .navbar-toggler {
    display: none;
  }
  .navbar-expand-lg .dropup .dropdown-menu {
    top: auto;
    bottom: 100%;
  }
}

Change @media (min-width: 992px) to @media (min-width:0px) and all responsiveness will be lost.

Save and minify and make sure you stylesheets are linked correctly.

Hope that helps :)

Hope that helps