scriptlevel

<math scriptlevel="-1"> <!-- decrease math-depth by 1 -->
<math scriptlevel="+2"> <!-- increase math-depth by 2 -->
<math scriptlevel="0"> <!-- reset math-depth to 0 -->

html,
body {
 height: 100%;
}
body {
 display: grid;
 place-items: center;
}
math {
 font-size: 24px;
}

<!-- math-depth defaults to 0 on the <math> root. -->
<math>
 <msubsup>
 <!-- math-depth and font-size remain unchanged on the base. -->
 <mtext>base</mtext>
 <!-- math-depth defaults to add(1) within the subscript, so it
 is incremented by 1 and the font-size is scaled down once. -->
 <mtext>subscript</mtext>
 <!-- math-depth defaults to add(1) within the superscript too, but
 the scriptlevel attribute tells to increment it by 2 instead,
 so the font-size is actually scaled down twice. -->
 <mtext scriptlevel="+2">superscript</mtext>
 </msubsup>
</math>

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