Receives computed CSS styles for the given element.
When requesting a single CSS property, its value will be returned as a string:
value = up.element.style(element, 'font-size')
// value is '16px'
When requesting multiple CSS properties, the function returns an object of property names and values:
value = up.element.style(element, ['font-size', 'margin-top'])
// value is { 'font-size': '16px', 'margin-top': '10px' }
One or more CSS property names in kebab-case or camelCase.