<!DOCTYPE html>
<title>Reference for WebVTT rendering, underline object transition with timestamp, ::cue(u:future) selector</title>
<style>
html { overflow:hidden }
body { margin:0 }
.video {
    display: inline-block;
    width: 1280px;
    height: 720px;
    position: relative
}
.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);
    font-size: 36px;
    text-decoration: underline;
    color: white;
}
.green {
    text-decoration: underline;
    color: #00ff00;
}
</style>
<div class="video"><span class="cue"><span>This is a <span class="green">test subtitle</span></span></span></div>