I didn't know either until I did this.
var element = document.createElement("div");
var count = 0;
for (var index in element.style) count++;
console.log(count); // 413

I didn't know either until I did this.
var element = document.createElement("div");
var count = 0;
for (var index in element.style) count++;
console.log(count); // 413

Can do instead
Object.keys(getComputedStyle(element)).length
know that some properties are only SVG related.
You would need to exclude non-CSS object properties to accurately count:
My browser (Chrome) has 439 ;-)