Dark Electric Blue (#536878)

/* Background */
.element {
    background-color: #536878;
}

/* Text */
.element {
    color: #536878;
}

/* Border */
.element {
    border: 1px solid #536878;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #536878,
        #9D7353
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #536878,
        #9D7353
    );
}

// SCSS variable
$dark-electric-blue: #536878;

// With RGB channels (useful for rgba() usage)
$dark-electric-blue-r: 83;
$dark-electric-blue-g: 104;
$dark-electric-blue-b: 120;

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