Does bootstrap 4 have a built in horizontal divider?

Question

HTML already has a built-in horizontal divider called <hr/> (short for "horizontal rule"). Bootstrap styles it like this:

hr {
  margin-top: 1rem;
  margin-bottom: 1rem;
  border: 0;
  border-top: 1px solid rgba(0, 0, 0, 0.1);
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" />
<p>
   Some text
   <hr/>
   More text
</p>

Bootstrap 4 define a CSS style for the HTML built-in horizontal divider <hr />, so just use it.

You can also customize margin with spacing utilities: mt for margin top, mb for margin bottom and my for margin top and bottom. The integer represent spacing 1 for small margin and 5 for huge margin. Here is an example:

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">

<hr class="mt-2 mb-3"/>
<!-- OR -->
<hr class="my-12"/>
<!-- It's like -->
<hr class="mt-3 mb-3"/>

I used to be using just a div with border-top like:

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">

<div class="border-top my-3"></div>

but it's a silly method to make the work done, and you can have some issues. So just use <hr />.

For Bootstrap 4

<hr> still works for a normal divider. However, if you want a divider with text in the middle:

<div class="row">
    <div class="col"><hr></div>
    <div class="col-auto">OR</div>
    <div class="col"><hr></div>
</div>

For dropdowns, yes:

https://v4-alpha.getbootstrap.com/components/dropdowns/

<div class="dropdown-menu">
  <a class="dropdown-item" href="#">Action</a>
  <a class="dropdown-item" href="#">Another action</a>
  <a class="dropdown-item" href="#">Something else here</a>
  <div class="dropdown-divider"></div>
  <a class="dropdown-item" href="#">Separated link</a>
</div>

For Bootstrap v4;

for a thin line;

<div class="divider"></div>

for a medium thick line;

<div class="divider py-1 bg-dark"></div>

for a thick line;

<div class="divider py-1 bg-dark"><hr></div>

You can use the mt and mb spacing utilities to add extra margins to the <hr>, for example:

<hr class="mt-5 mb-5">

https://getbootstrap.com/docs/4.3/utilities/spacing/

Here are some custom utility classes:

hr.dashed {
    border-top: 2px dashed #999;
}

hr.dotted {
    border-top: 2px dotted #999;
}

hr.solid {
    border-top: 2px solid #999;
}


hr.hr-text {
  position: relative;
    border: none;
    height: 1px;
    background: #999;
}

hr.hr-text::before {
    content: attr(data-content);
    display: inline-block;
    background: #fff;
    font-weight: bold;
    font-size: 0.85rem;
    color: #999;
    border-radius: 30rem;
    padding: 0.2rem 2rem;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}



/*
*
* ==========================================
* FOR DEMO PURPOSES
* ==========================================
*
*/

body {
    min-height: 100vh;
    background-color: #fff; 
    color: #333;
}
.text-uppercase {
  letter-spacing: .1em;
}

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.2/css/bootstrap.min.css">

<div class="container py-5">
    <!-- For Demo Purpose -->
    <header class="py-5 text-center">
        <h1 class="display-4">Bootstrap Divider</h1>
        <p class="lead mb-0">Some divider variants using &lt;hr&gt; element.    </p>
    </header>


    <div class="row">
        <div class="col-lg-8 mx-auto">
            <div class="mb-4">
                <h6 class=" text-uppercase">Dashed</h6>
                <!-- Dashed divider -->
                <hr class="dashed">
            </div>
            <div class="mb-4">
                <h6 class=" text-uppercase">Dotted</h6>
                <!-- Dotted divider -->
                <hr class="dotted">
            </div>
            <div class="mb-4">
                <h6 class="text-uppercase">Solid</h6>
                <!-- Solid divider -->
                <hr class="solid">
            </div>
            <div class="mb-4">
                <h6 class=" text-uppercase">Text content</h6>
                <!-- Gradient divider -->
                <hr data-content="AND" class="hr-text">
            </div>
           
        </div>
    </div>
</div>