JSFiddle - React, Tailwind, and code Playground

HTML

<div class="starttour">
    <div class="newbutton headerbutton"> <span class="iconhead icon-02-arrow-icon"></span></div>
    <p>START TOUR</p>
</div>

CSS

.newbutton {
    border-radius: 50%;
    width: 74px;
    height: 74px;
    position: relative;
    background-color: black;
    margin: 60px 0px 25px 17px;
    overflow: visible;
}
.newbutton::before {
    content:"f";
    width:80px;
    height:80px;
    position: absolute;
    border-radius:50%;
    z-index:-1;
    top:37px;
    left:37px;
    -webkit-transform:translate(-50%, -50%);
    transform:translate(-50%, -50%);
    -webkit-animation-name: fadecolor;
    -webkit-animation-duration: 5s;
    -webkit-animation-iteration-count: infinite;
    animation-name: fadecolor;
    animation-duration: 5s;
    animation-iteration-count: infinite;
}
.newbutton::after {
    content:""!important;
    width: 80px;
    height: 80px;
    position: absolute;
    border-radius: 50%;
    z-index: -2;
    top: -3px;
    left: -3px;
    background: -webkit-gradient(linear, 0% 0%, 0% 100%, from(#01BAE8), to(#0183D5));
}

JavaScript

(function () {
   
    var el = document.querySelector( ".newbutton" );
    
    [ "", "::before", "::after" ].forEach(function ( e ) {
        console.log( window.getComputedStyle( el, e ).height );
    });
    
}());