<!DOCTYPE html>
<title>Reference for WebVTT rendering, ::cue(u), outline properties</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;
}
.cue > span > u {
    display: inline-block;
    margin-left: -2px;
    margin-right: -2px;
    border: solid #00f 2px;
    border-bottom: none;
}
</style>
<div class="video"><span class="cue"><span>This is a <u>test subtitle</u></span></span></div>