Look what I just realized! Paste the following into a tiddler. You might want to play around with the width of the story river also:
So the text starts out with some unsignificant stuff of no importance. But then... <span class="encircle">this is the really important stuff inside the text that really needs highlighting in some way so it is encircled as if it was done with a marker pen! </span> And then then unimportant text can continue afterwards as if nothing happened.
<style>
.encircle {
outline:5px solid #ff000080;
outline-offset:2px;
border-radius:50%;
}
</style>