Check whether plugin works with only one style element (no further merging needed, noop).

===

<svg id="test" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
    <style>
        .st0{ fill:red; padding-top: 1em; padding-right: 1em; padding-bottom: 1em; padding-left: 1em; }
    </style>
    <rect width="100" height="100" class="st0" style="stroke-width:3;margin-top:1em;margin-right:1em;margin-bottom:1em;margin-left:1em"/>
</svg>

@@@

<svg id="test" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
    <style>
        .st0{ fill:red; padding-top: 1em; padding-right: 1em; padding-bottom: 1em; padding-left: 1em; }
    </style>
    <rect width="100" height="100" class="st0" style="stroke-width:3;margin-top:1em;margin-right:1em;margin-bottom:1em;margin-left:1em"/>
</svg>