@grin3671,

@font-face {
  font-family: FontAwesome;
  font-style: normal;
  font-weight: 900;
  src: url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.eot);
  src: url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.eot?#iefix) format('embedded-opentype'),
       url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.woff2) format('woff2'),
       url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.woff) format('woff'),
       url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.ttf) format('truetype'),
       url(https://use.fontawesome.com/releases/v5.15.3/webfonts/fa-solid-900.svg#fontawesome) format('svg');
}

.fa-icon {
  font-family: FontAwesome;
}

.fa-icon[data-icon="cog"]::before {
  content: ''; /* Copy Glyph */
  content: '\f013'; /* Обратный слеш + Copy Unicode */
}

[div=fa-icon data-icon=cog][/div]

Список иконок: fontawesome.com
Страница иконки из примера: fontawesome.com