Solution 1 :

You should use input-group-addon and remove class form-control

Like

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css" rel="stylesheet"/>
<div class="container"> 
    <div class="row">
        <div class="input-group">
            <div class="input-group-addon">
                <span class="input-group-text">Caption<br/></span>
            </div>
            <span>
                <p class="form-control">Line 1</p>
                <p class="form-control"><strong>Line 2</strong></p>
                <p class="form-control"><strong>Line 3</strong></p>
            </span>
        </div>
    </div>
</div>

Fiddle http://jsfiddle.net/bL6t8vrg/1/

Solution 2 :

You can use the following using a list-group with list-group-item and some customs rules to remove the inner border-radius (between prepend label and rows).

.input-group .list-group .list-group-item {
  border-top-left-radius: 0px;
  border-bottom-left-radius: 0px;
}
.input-group .input-group-prepend {
  border-top-right-radius: 0px;
  border-bottom-right-radius: 0px;
}
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">

<div class="container"> 
  <div class="row">
    <div class="input-group mb-2 col-12">
      <div class="input-group-prepend">
        <span class="input-group-text">Caption<br/></span>
      </div>
      <ul class="list-group">
        <li class="list-group-item">Line 1</li>
        <li class="list-group-item"><strong>Line 2</strong></li>
        <li class="list-group-item"><strong>Line 3</strong></li>
      </ul>
    </div>
  </div>
</div>

Problem :

I’m new to Bootstrap and I’m trying to create an HTML form using Bootstrap input-groups with input-group-prepend captions. I need to be able to create a row with a single pre-pended caption with multiple styled lines within the associated form-control element, as shown below:

enter image description here

My HTML attempt looks like this so far:

<div class="container"> 
    <div class="row">
        <div class="input-group mb-2 col-12">
            <div class="input-group-prepend">
                <span class="input-group-text">Caption<br/></span>
            </div>
            <span class="form-control">
                <p>Line 1</p>
                <p><strong>Line 2</strong></p>
                <p><strong>Line 3</strong></p>
            </span>
        </div>
    </div>
</div>

with the following result:
enter image description here

How can I get multiple lines in the right-hand section within the bordered area? Any suggestions greatly appreciated.

Comments

Comment posted by Flandiddly

Thanks for the quick reply Kenny. Your answer solves the multi-line issue but the borders are lost on the right-hand side. Any idea how I can retain them?

Comment posted by Kenny

You need to give class

By