How can i add style to the element in javascript?

I have this piece of code inside my javascript, I want to select the element by the class name and then be able to style it, how can I do that?

const versesHtml = `              
                ${verses.map( (v, i) => `<li class="text">${v.text_uthmani}</li> <li class="ayahNumber">{${i+1}}</li>`).join(' ')}
               
                
               
            `;

>Solution :

var elements = document.getElementsByClassName('ayahNumber'); // get all elements
    for(var i = 0; i < elements.length; i++){
        elements[i].style.backgroundColor = "black";
    }