Green-cyan (#009966)

/* Background */
.element {
    background-color: #009966;
}

/* Text */
.element {
    color: #009966;
}

/* Border */
.element {
    border: 1px solid #009966;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #009966,
        #FF3377
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #009966,
        #FF3377
    );
}

// SCSS variable
$green-cyan: #009966;

// With RGB channels (useful for rgba() usage)
$green-cyan-r: 0;
$green-cyan-g: 153;
$green-cyan-b: 102;

// Usage
.element {
    background-color: $green-cyan;
    color: rgba($green-cyan-r, $green-cyan-g, $green-cyan-b, 0.8);
}