Logout buttons for Bootstrap or Bulma <nav> elements

Re Bootstrap, what does your HTML look like?

Re Bulma, there is no space between the buttons because the rule that adds it expects .nav-item .button + .button:

.nav-item .button + .button {
    margin-left: 10px;
}

Something like this should work:

<a class="button is-info" style="margin-left: 10px;">Sign up</a>