HTML color codes are hexadecimal triplets representing the colors red, green, and blue (#RRGGBB). HTML color code has six hex values (e.g #AADDBB). Those six letters represent 2 for red, 2 for green and 2 for blue. And also, the value begin from 00 to ff (minimum to maximum).
CSS stands for Cascading Style Sheets.CSS is a language that you can use to define styles against any HTML element. These styles are set using CSS properties.For example, you can set font properties (size, colors, style etc), background images, border styles, and much more.Using CSS, We can define all our common styles in an external Style Sheet.