What Is the '. Well' Equivalent Class in Bootstrap 4

Wells are dropped from Bootstrap with the version 4.

You can use Cards instead of Wells.

Here is a quick example for how to use new Cards feature:

<div class="card card-inverse" style="background-color: #333; border-color: #333;">
  <div class="card-block">
    <h3 class="card-title">Card Title</h3>
    <p class="card-text">This text will be written on a grey background inside a Card.</p>
    <a href="#" class="btn btn-primary">This is a Button</a>
  </div>
</div>

This worked best for me:

<div class="card bg-light p-3">
 <p class="mb-0">Some text here</p>
</div>

None of the answers seemed to work well with buttons. Bootstrap v4.1.1

<div class="card bg-light">
    <div class="card-body">
        <button type="submit" class="btn btn-primary">
            Save
        </button>
        <a href="/" class="btn btn-secondary">
            Cancel
        </a>
    </div>
</div>

Sure officially version says the cards are the new replacements for Bootstrap wells. But Cards are a quite broad Bootstrap components now. In simple terms, you can also use Bootstrap Jumbotron too.

Looking for a one line option:

    <div class="jumbotron bg-dark"> got a team? </div>        

I'm mading my classes well for class alert, for me it looks like it's getting nice, but some tweaks are sometimes needed as to put the width 100%

<div class="alert alert-light" style="width:100%;">
  <strong>Heads up!</strong> This <a href="#" class="alert-link">alert needs your attention</a>, but it's not super important.
</div>

Card seems to be "discarded" LOL, I found the "well" not working with bootstrap 4.3.1 and jQuery v3.4.1, just working fine with bootstrap 4.3.1 and jQuery v3.3.1. Hope it helps.