RGB is an additive color model which represents colors as mixtures of red, green, and blue light. In essence, the RGB representation is the decimal equivalent of the Hexadecimal Notation. In Hexadecimal each number ranges from 00-FF which is equivalent to 0-255 in decimal and 0%-100% in percentages.

.some-class {
    /* Scalar RGB, equivalent to 'blue'*/
    color: rgb(0, 0, 255);
}

.also-blue {
    /* Percentile RGB values*/
    color: rgb(0%, 0%, 100%);
}

Syntax

rgb(<red>, <green>, <blue>)

Value | Description | —— | —— |<red> | an integer from 0 - 255 or percentage from 0 - 100% |<green> | an integer from 0 - 255 or percentage from 0 - 100% |<blue> | an integer from 0 - 255 or percentage from 0 - 100% |