adrianosoarez

Hello Budi2000,
I was also having this difficulty and I decided this way:

add it to the post editor (Text Tab) for example:

<ol class="letters">
  <li>Coffee</li>
  <li>Tea</li>
  <li>Milk</li>
 </ol>

and add custom css

Appearance > Customize > Advanced options > Additional CSS

just copy and paste the code and publish

.entry ol.letters li {
list-style-type: lower-alpha!important;
}

sorry for the language, i used google translate
to answer you.