CSS\HTML - How to add Ionicons to CSS "content" property?

Question

I'm using a custom switch toggle (from here) and I want to add an icon instead of regular text. When I paste the Ionicons code to the CSS content property it appears as a rectangle (some indication for the fact the character\font was not found). How do I get pass this?

EDIT: I forgot to add, I have included the CSS from CDN.

JSfiddle

Switch CSS:

.onoffswitch {
    position: relative; 
    width: 108px;
    -webkit-user-select:none; 
    -moz-user-select:none; 
    -ms-user-select: none;
}
.onoffswitch-checkbox {
    display: none;
}
.onoffswitch-label {
    display: block; 
    overflow: hidden; 
    cursor: pointer;
    border: 2px solid #999999; 
    border-radius: 30px;
}
.onoffswitch-inner {
    display: block; 
    width: 200%; 
    margin-left: -100%;
    -moz-transition: margin 0.3s ease-in 0s; 
    -webkit-transition: margin 0.3s ease-in 0s;
    -o-transition: margin 0.3s ease-in 0s; 
    transition: margin 0.3s ease-in 0s;
}
.onoffswitch-inner:before, .onoffswitch-inner:after {
    display: block; 
    float: left; width: 50%; 
    height: 40px; padding: 0; 
    line-height: 38px;
    font-size: 14px; 
    color: white; 
    font-weight: bold;
    -moz-box-sizing: border-box; 
    -webkit-box-sizing: border-box; 
    box-sizing: border-box;
}
.onoffswitch-inner:before {
    content: "ON";
    padding-left: 10px;
    background-color: #FFFFFF; 
    color: #BABABA;
}
.onoffswitch-inner:after {
    content: "\f425"; /* <--------THE ICON GOES HERE */
    padding-right: 10px;
    background-color: #8035A7; 
    color: #FFFFFF;
    text-align: right;
}
.onoffswitch-switch {
    display: block; 
    width: 41px; margin: -1.5px;
    background: #FFFFFF;
    border: 2px solid #999999; 
    border-radius: 50px;
    position: absolute; 
    top: 0; 
    bottom: 0; 
    right: 66px;
    -moz-transition: all 0.3s ease-in 0s; 
    -webkit-transition: all 0.3s ease-in 0s;
    -o-transition: all 0.3s ease-in 0s; 
    transition: all 0.3s ease-in 0s; 
}
.onoffswitch-checkbox:checked + .onoffswitch-label .onoffswitch-inner {
    margin-left: 0;
}
.onoffswitch-checkbox:checked + .onoffswitch-label .onoffswitch-switch {
    right: 0px; 
}

HTML:

    <div class="onoffswitch">
        <input type="checkbox" name="onoffswitch" class="onoffswitch-checkbox" id="myonoffswitch" checked>
        <label class="onoffswitch-label" for="myonoffswitch">
            <p id="impressions_meter_text">Impressions meter</p>
            <span class="onoffswitch-inner"></span>
            <span class="onoffswitch-switch"></span>
        </label>
    </div>

Answer 1

You're missing a @font-face declaration that imports the "Ionicons" font face, plus the .onoffswitch-inner:after declaration doesn't specify the font-family: "Ionicons";.

I've extracted the Ionicons font declaration from their css and added it to a forked jsFiddle.