Why the author's font may not be adequately displayed?

Question

css

Download the font in .ttf format, it is displayed normally when installed on the computer, as it should, I put on the site something completely different, what could be the reason?

@font-face {
    font-family: 'headingpro-extrabolditalic';
  src: url("/fonts/Heading-Pro-ExtraBold-Italic.ttf") format("ttf");
    font-weight: normal;
    font-style: normal;
}
body {
  font-family: 'headingpro-extrabolditalic';
}