Ultramarine Blue (#4166F5)

/* Background */
.element {
    background-color: #4166F5;
}

/* Text */
.element {
    color: #4166F5;
}

/* Border */
.element {
    border: 1px solid #4166F5;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #4166F5,
        #FCF9EE
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #4166F5,
        #FCF9EE
    );
}

// SCSS variable
$ultramarine-blue: #4166F5;

// With RGB channels (useful for rgba() usage)
$ultramarine-blue-r: 65;
$ultramarine-blue-g: 102;
$ultramarine-blue-b: 245;

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