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HTML 

              
                <!--
This is a demo of how to use Font Awesome icons via CSS pseudo-elements. Read more about the techniques in this demo at https://fontawesome.com/docs/web/add-icons/pseudo-elements#css-pseudo-elements-and-duotone
-->

<html>
<head>
  <title>Font Awesome: CSS PSeudo Elements and Duotone Icons</title>
  
  <!-- We're using a Pro WebFont Kit to load Font Awesome Version 6 Latest -->
<script src="https://kit.fontawesome.com/a24879a822.js" crossorigin="anonymous"></script></head>
</head>

<body>
  <main class="demo-frame">
      <h2>Adding Duotone Icons with CSS Pseudo Elements</h2>
    <section class="demo">
      <article class="demo-example">

        
        <!-- The code for this feature showcase starts here -->
        
        <p class="icon-duotone rabbit-icon">Regular Duotone Icon</p>
        
        <p class="icon-duotone custom-icon-duotone magic">Custom Duotone Icon</p>

        <p class="icon-duotone custom-icon-duotone portal">Custom Duotone Icon</p>
                
        
        <!-- The code for this feature showcase end here -->
        
      </article>  
    </section>    
  </main> 
</body>
</html>
!

CSS 

              
                /* CSS styling for your issue */


  /* Step 1: Common Duotone positioning properties: All required to make icons render reliably */
  .icon-duotone {
    position: relative;
    padding-left: 1.25em; /* make space for the width of the absolutely positioned icon */
  }

  /* Step 2: Set the font styles for Duotone */
  .icon-duotone::before,
  .icon-duotone::after {
    font: var(--fa-font-duotone);

    /* include the basic Font Awesome font style settings if you haven't already */
    display: inline-block;
    text-rendering: auto;
    -webkit-font-smoothing: antialiased;

    /* position both layers of the icon to the left, set our fixed-width width, horizontally center layers, and then vertically align them so they flex with different line heights */
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 1.25em;
    text-align: center;
  }

  /* Step 3: Set the default opacity levels and colors for each layer */
  .icon-duotone::before {
    color: var(--fa-primary-color, inherit);
    opacity: 1;
    opacity: var(--fa-primary-opacity, 1.0);
  }

  .icon-duotone::after {
    color: var(--fa-secondary-color, inherit);
    opacity: var(--fa-secondary-opacity, 0.4);
  }

  /* Step 4: Reference an individual icon's layers using unicodes */
  /* This rule renders the primary duotone for the rabbit icon */
  .icon-duotone.rabbit-icon::before {
    content: "\f708";
  }

  /* This rule renders the secondary duotone for the rabbit icon */
  .icon-duotone.rabbit-icon::after {
    content: "\f708\f708";
  }

  /* Below are rules for using Custom Duotone Icons as pseudo elements */
  /* First, include the rules in Step 1, 2, and 3 above which are needed for all Duotone icons */
  /* Step 4: Set the font-family for Custom Duotone Icons */
  .custom-icon-duotone::before,
  .custom-icon-duotone::after {
    font-family: "Font Awesome Kit Duotone"; /* note that you need to use "font-family" for custom icons */
  }

  /* Step 5: Reference an individual custom icon's layers using unicodes */
  /* This rule renders the primary duotone for the custom magic icon */
  .custom-icon-duotone.magic::before {
    content: "\e006"; /*  replace with your custom icon's unicode value */
  }

  /* This rule renders the secondary duotone for the custom magic icon */
  .custom-icon-duotone.magic::after {
    content: "\e006\e006"; /*  replace with your custom icon's unicode value, twice */
  }


  /* you can also set individual colors for each layer or adjust layer opacity */
  /* This rule renders the primary duotone for the custom magic icon */
  .custom-icon-duotone.portal::before {
    content: "\e007"; /*  replace with your custom icon's unicode value */
    color: black;
  }

   /* This rule renders the secondary duotone for the custom magic icon */
  .custom-icon-duotone.portal::after {
    content: "\e007\e007"; /*  replace with your custom icon's unicode value, twice */
    color:  Violet;
    opacity: .7;
  }
 




/* demo styling - ignore */
.demo-example {
  font-size: 1.5rem;
}
!

JS 

              
                /* JS for this feature */
!
999px

Console