#hue {
height: 40px;
--lightness: 50%;
background: linear-gradient(90deg,
hsl(0, 100%, calc(var(--lightness) * 1.30)),
hsl(15, 100%, calc(var(--lightness) * 1.10)),
hsl(35, 100%, calc(var(--lightness) * 1.02)),
hsl(48, 100%, calc(var(--lightness) * 0.90)),
hsl(60, 100%, calc(var(--lightness) * .76)),
hsl(72, 100%, calc(var(--lightness) * .71)),
hsl(90, 100%, calc(var(--lightness) * .70)),
hsl(105, 100%, calc(var(--lightness) * .70)),
hsl(120, 100%, calc(var(--lightness) * .695)),
hsl(135, 100%, calc(var(--lightness) * .70)),
hsl(150, 100%, calc(var(--lightness) * .70)),
hsl(165, 100%, calc(var(--lightness) * .69)),
hsl(180, 100%, calc(var(--lightness) * .65)),
hsl(195, 80%, calc(var(--lightness) * .85)),
hsl(215, 75%, calc(var(--lightness) * 1.25)),
hsl(225, 100%, calc(var(--lightness) * 1.40)),
hsl(240, 100%, calc(var(--lightness) * 1.48)),
hsl(255, 100%, calc(var(--lightness) * 1.44)),
hsl(270, 100%, calc(var(--lightness) * 1.35)),
hsl(285, 100%, calc(var(--lightness) * 1.15)),
hsl(300, 90%, calc(var(--lightness) * .89)),
hsl(315, 80%, calc(var(--lightness) * .98)),
hsl(330, 90%, calc(var(--lightness) * 1.12)),
hsl(345, 95%, calc(var(--lightness) * 1.21)),
hsl(360, 100%, calc(var(--lightness) * 1.30))
);
}
<div id="hue"></div>