How to put only a bottom border using bootstrap.(Portfolio Project)

I’m trying to add the horizontal line that’s between the paragraph and span elements in the project example. I tried copying the example but it wouldn’t work. It looks like he used , it didn’t help, however. Any help would be fantastic and might earn you some Karma points.

Example page:

<!DOCTYPE html>
<html lang="en">
  <!--  Meta  -->
  <meta charset="UTF-8" />
  <title>My Portfolio Site</title>
  <!--  Styles  -->
  <link rel="stylesheet" href="" integrity="sha384-PsH8R72JQ3SOdhVi3uxftmaW6Vc51MKb0q5P2rRUpPvrszuE4W1povHYgTpBfshb" crossorigin="anonymous">
  <link rel="stylesheet" href=">
  <link rel="stylesheet" type="text/css" href="styles/style.css">
<body style="background-color: #581845;">  
<div class="container-fluid">
  <div class="row">
    <div class="col-md-12 bg-primary sticky-top">
      <div class="mx-auto col-md-9 navbar bg-primary">
        <a class="nav-item mr-auto" href="#top"><img src="" style="max-height:5em"></a>  
        <a class="nav-item nav-link text-white" href="#about">About</a>
        <a class="nav-item nav-link text-white" href="#portfolio">Portfolio</a>
        <a class="nav-item nav-link text-white" href="#contact">Contact</a>
  <div class="container bg-secondary rounded p-5 mt-5" id="about">
      <div class="row"                                         
      <div class="intro-text m-auto p-auto col-xs-8">    
        <p class="text-center m-auto lead">Musician, creator, and student of web development. My hope is to help bridge the technological gap for authors, artists, and other creative beings to bring awareness to their work.</p>                                                 

Open to all suggestions, even those unrelated to the specific question!

Hi, friend @kyleshamblin. You can use the <hr> tag between span and paragraph.