It works fine with the default callout icons, so it appears that it doesn’t work with custom SVGs… In this case you have to do something like this:
.callout[data-callout="book-love"] { ... your existing code ... }
/* enlarge the icon */
.callout[data-callout="book-love"] .callout-icon {
width: 42px;
height: 42px;
transform-origin: left;
transform: scale(2.5);
}
But you have to play with the scale, width & height until you find what you’re after.