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 function, 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 data type.... or quotes, unless these characters are escaped, or if the address...address includes control characters above 0x7e. Double quotes...