Between below two there is no difference.
color:#fff;
or
color:#FFF;
CSS Color Codes
Go for : #FFFFFF this kind of hexa color than rather than short hand.
In CSS, you define a color using either the hexadecimal color code, the RGB color code, or the actual color name. A benefit of using hexadecimal and RGB color codes is that you have many more options than just supplying a color name.
The color picker and chart on this page provide you with the hexadecimal color codes. The color picker also provides the RGB color code.
Hexadecimal color codes are often referred to as "hexadecimal colors", "hex colors codes", "color values" and a few other terms. "Hexadecimal color values" is probably the most accurate term as they are made up of hexadecimal numbers.