※★CSS
span.sample1 {
vertical-align: super;
background-color:#ffccff;
}
span.sample2 {
vertical-align: sub;
background-color:#ffccff;
}
※★HTML
<p>100m<span class="sample1">2</span></p>
<p>H<span class="sample2">2</span>O</p>
100m2
H2O