mermaid/src/themes/pie.scss

.pieTitleText {
  text-anchor: middle;
  font-size: 25px;
  fill: $taskTextDarkColor;
  font-family: 'trebuchet ms', verdana, arial;
  font-family: var(--mermaid-font-family);
}
.slice {
  font-family: 'trebuchet ms', verdana, arial;
  font-family: var(--mermaid-font-family);
}