I try to animate `content` property of ::before pseudoelement.
I set the content property in rule and change its value in keyframes.
It works correct in Firefox and Chrome, but doesn't work in Safari.
Spec says https://drafts.csswg.org/css-transitions/#animatable-properties
"…since the from and to values cannot be interpolated, the animation is done in a single step."
You can watch the bug here: https://codepen.io/juwain/pen/JLozbJ