Fluorescent Yellow (#CCFF00)

/* Background */
.element {
    background-color: #CCFF00;
}

/* Text */
.element {
    color: #CCFF00;
}

/* Border */
.element {
    border: 1px solid #CCFF00;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #CCFF00,
        #3300FF
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #CCFF00,
        #3300FF
    );
}

// SCSS variable
$fluorescent-yellow: #CCFF00;

// With RGB channels (useful for rgba() usage)
$fluorescent-yellow-r: 204;
$fluorescent-yellow-g: 255;
$fluorescent-yellow-b: 0;

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