Grab CSS property for given locator
Resumes test execution, so **should be used inside an async function with `await`** operator.
If more than one element is found - value of first element is returned.

```js
const value = await I.grabCssPropertyFrom('h3', 'font-weight');
```

@param {CodeceptJS.LocatorOrString} locator element located by CSS|XPath|strict locator.
@param {string} cssProperty CSS property name.
@returns {Promise<string>} CSS value