Warm Black (#004242)

/* Background */
.element {
    background-color: #004242;
}

/* Text */
.element {
    color: #004242;
}

/* Border */
.element {
    border: 1px solid #004242;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #004242,
        #840000
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #004242,
        #840000
    );
}

// SCSS variable
$warm-black: #004242;

// With RGB channels (useful for rgba() usage)
$warm-black-r: 0;
$warm-black-g: 66;
$warm-black-b: 66;

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