<!DOCTYPE html>
<title>Reference for WebVTT rendering, voice object with class, ::cue(v.foo) selector</title>
<style>
html { overflow:hidden }
body { margin:0 }
.video {
    display: inline-block;
    width: 320px;
    height: 180px;
    position: relative;
    font-size: 9px;
}
.cue {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    text-align: center
}
.cue > span {
    font-family: sans-serif;
    background: rgba(0,0,0,0.8);
    color: white;
}
.green {
    color: #00ff00;
}
</style>
<div class="video"><span class="cue"><span>This is a <span>test subtitle</span>, <span class="green">test subtitle</span></span></span></div>