I am using the premailer-rails gem in my Rails app and it fails to process CSS variables. I am using Bulma CSS.

For example, I have a tag <h1 class="title is-1">Welcome</h1>

In the email sent, it converts it to:

<h1 style="
  font-size:3rem;
  font-weight:var(--bulma-content-heading-weight);
  box-sizing:inherit;
  color:var(--bulma-content-heading-color);
  line-height:var(--bulma-content-heading-line-height);
  word-break:break-word;
  padding:0">Welcome to Shoe Sensei!</h1>

Notice how the font-size, box-sizing, word-break, and padding values are correctly assigned.

But the font-weight, color, and line-height values are kept as var(...).

Can I get some help fixing this, please?