ค่าระหว่าง 1000px-700px จะแสดง คำว่า email
(max-width: 1000px) and (min-width: 700px)

<style>
ul {
    list-style-type: none;
}

ul li a {
    color: green;
    text-decoration: none;
    padding: 3px; 
    display: block;
}

@media screen and (max-width: 699px) and (min-width: 520px) {
    ul li a {
        padding-left: 30px;
        background: url(email-icon.png) left center no-repeat;
    }
}

@media screen and (max-width: 1000px) and (min-width: 700px) {
    ul li a:before {
        content: "Email: ";
        font-style: italic;
        color: #666666;
    }
}

@media screen and (min-width: 1001px) {
    ul li a:after {
        content: " (" attr(data-email) ")";
        font-size: 12px;
        font-style: italic;
        color: #666666;
    }
}
</style>

<ul>
  <li><a data-email="johndoe@example.com" href="mailto:johndoe@example.com">John Doe</a></li>
  <li><a data-email="marymoe@example.com" href="mailto:marymoe@example.com">Mary Moe</a></li>
  <li><a data-email="amandapanda@example.com" href="mailto:amandapanda@example.com">Amanda Panda</a></li>
</ul>

https://en.support.wordpress.com/custom-design/custom-css-media-queries/
https://premium.wpmudev.org/blog/how-to-customize-responsive-wordpress-themes-part-4-media-queries/