How to change spacing between letters

Add the following CSS to design customizations:

.page {
  letter-spacing: 0.1px;
}

You can change .page to e.g. .page-title or something else to change the spacing only for headers or other elements.

To apply it only on mobile, use media queries. In the following example it will apply only for screens with the width less than 760px:

@media (max-width: 760px) {
  .page {
    letter-spacing: 0.1px;
  }
}