用那条绿线做background-image, background-position设置为left bottom，效果:

更新一下：不用图片
1. HTML：

<p id="test">123456</p>

2. CSS

#test { width: 104px; height: 30px; border-bottom: 5px solid #5DD301; position: relative; }
#test:after { content: ''; display: block; width: 5px; height: 5px; background-color: #1C7600; position: absolute; bottom: -5px; }