EmojiOne font does not work

Question

I want to show all Emojis in my HTML page with the font EmojiOne. Therefore I gave the class emoji to all the divs and spans which consist of emojis. In my css I imported the font "EmojiOne" and assigned that font to the class Emoji.

<div class="emoji"></div>

@font-face {
font-family: EmojiOne;
src: url(./emojione-svg.otf);
}
.emoji{
  font-family: EmojiOne, Helvetica, sans-serif;  
}

The text with the class emoji is not shown in EmojiOne but Helvetica.