You can do this using CSS counters, in conjunction with the :before
pseudo element:
ol {
list-style: none;
counter-reset: item;
}
li {
counter-increment: item;
margin-bottom: 5px;
}
li:before {
margin-right: 10px;
content: counter(item);
background: lightblue;
border-radius: 100%;
color: white;
width: 1.2em;
text-align: center;
display: inline-block;
}
<ol>
<li>item</li>
<li>item</li>
<li>item</li>
<li>item</li>
</ol>