JSFiddle - React, Tailwind, and code Playground

HTML

<p id="some_element">Something</p>

CSS

#some_element {
    border:1px solid rgb(255,0,0);
}

JavaScript

el_style = window.getComputedStyle(document.getElementById('some_element'));
el_border_color = el_style.getPropertyValue('border-color');
alert(el_border_color);