When i was a little kid, I was really scared of the dark. But then I came to understand, dark just means the absence of photons in the visible wavelength -- 400 to 700 nanometers. Then i thought, well, its really silly to be afraid of a lack of photons. Then i wasn't afraid of the dark anymore after that.
Elon Musk

url()

The url() CSS function is used to include a file. The parameter is an absolute URL, a relative URL, a blob URL, or a data URL. The url() function can be passed as a parameter of another CSS functions, like the attr() function. Depending on the property for which it is a value, the resource sought can be an image, font, or a stylesheet. The url() functional notation is the value for the <url> data type.
<url> css reference