/* With a lot of Firefox dev tools exploration, I figured out how Wikipedia does its chemical formulas. Example:
 * https://en.wikipedia.org/wiki/Carbonate
 */
.chem {
    display: inline-block;
    line-height: 0.6;
    vertical-align: -0.25em
}
.chem > span {
    display: block;
    line-height: 1;
}
.sup {
    font-size: 70%;
    line-height: 0.6;
    vertical-align: 0.60em
}
.sub {
    font-size: 70%;
    line-height: 0.6;
    vertical-align: -0.25em
}

/* Fraction bar code source:
 * https://www.periodni.com/mathematical_and_chemical_equations_on_web.html
 */
.fr {
    display: inline-block;
    vertical-align: middle; 
    margin: 0 0.2em 0.4ex;
    text-align: center;
}
.fr > span {
    display: block;
    padding-top: 0.15em;
}
.fr span.fd {border-top: thin solid #FFFFFF;}
.fr span.fb {display: none;}