[s4i]

You could namespace the Pico styles using SASS. Basically like [1] but you'd extend it to be e.g.

  .pico-enabled *:not(.piko-disabled) {
    @import "layout/document"
    @import "layout/sectioning"
    @import "layout/container"
    ...

Then you can do this:

  <div class="piko-enabled">
    ...
    <button>A button with Piko styling</button>
    <div class="piko-disabled">
      <button>A vanilla browser button</button>
      ... and any 3rd party components/elements etc ...

[1] https://github.com/picocss/pico/issues/31#issuecomment-91399...