Navy Blue (#000080)

/* Background */
.element {
    background-color: #000080;
}

/* Text */
.element {
    color: #000080;
}

/* Border */
.element {
    border: 1px solid #000080;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #000080,
        #FFFF01
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #000080,
        #FFFF01
    );
}

// SCSS variable
$navy-blue: #000080;

// With RGB channels (useful for rgba() usage)
$navy-blue-r: 0;
$navy-blue-g: 0;
$navy-blue-b: 128;

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