CSS/アンダーライン

#underline {
  position: relative;
  font-size: 30px;
  margin: 50px 0 20px 30px;
}
#underline:after {
  position: absolute;
  bottom: 10px;
  left: 0;
  z-index: 0;
  content: '';
  width: 210px;
  height: 10px;
  background: rgba(210,50,14,0.5);
}

#underline02 {
	position: relative;
	font-size: 30px;
	margin: 50px 0 20px 30px;
}
#underline02:after {
	position: absolute;
	bottom: 0px;
	left: -10px;
	z-index: 0;
	content: '';
	width: 270px;
	height: 35px;
	background: rgba(10,150,14,0.3);
}