Another possibility:
p {
font-size: 100px;
font-family: arial;
}
span {
padding: 0 10px;
box-shadow: inset 0 -40px 0 0 magenta;
}
span:nth-child(2) {
box-shadow: inset 0 -55px 0 0 magenta;
}
span:nth-child(3) {
box-shadow: inset 0 -70px 0 0 magenta;
}
<p>
<span>A</span><span>B</span><span>C</span>
</p>