<div class="element">
  <div class="box primary">Primary Box</div>
  <div class="box secondary">Secondary Box</div>
</div>

<div class="form">
  <div class="control">
    <label for="h">H:</label>
    <input type="range" min="0" max="360" name="color" step="1" id="h" value="80" />
  </div>
  <div class="control">
    <label for="s">S:</label>
    <input type="range" min="0" max="100" name="color" step="1" id="s" value="20" />
  </div>
  <div class="control">
    <label for="l">L:</label>
    <input type="range" min="0" max="100" name="color" step="1" id="l" value="60" />
  </div>
</div>
@import url("https://fonts.googleapis.com/css?family=Gochi+Hand");

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}


body {
  width: 100vw;
  height: 100vh;
  margin: 0;
  padding: 0;
  background-color: #291642;
  font-family: "Gochi Hand", sans-serif;
  font-size: 130%;
  letter-spacing: 0.1rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.element {
  padding: 10vmin 20vmin;
  display: flex;
  justify-content: center;
  background-image: radial-gradient(circle at center, hsl(var(--h) calc(var(--s) * 1%) calc(var(--l) * 1%)), #291642),
    linear-gradient(to bottom, #291642, #291642);
  background-repeat: no-repeat;
  background-position: center;
  background-clip: padding-box;
  border-radius: 8px;
  background-blend-mode: multiply, screen;
  margin-bottom: 10px;
}

.box {
  border-radius: 2vmin;
  padding: 5vmin;
  margin:0 3vmin;
  white-space: nowrap;
  font-size: 2rem;
}

.form {
  display: flex;
  align-items: center;
  color: #fff;
}

.control {
  margin: 4vmin;
  display: flex;
  align-items: center;
  font-size: 3rem;
}

:root {
  --h: 80;
  --s: 20;
  --l: 60;
  --threshold: 65;
  --border-threshold: 80;
}


.box {
  --hue: var(--h);
  --switch: calc((var(--l) - var(--threshold)) * -100%);
  --border-light: calc(var(--l) * 0.7%);
  --border-alpha:calc((var(--l) - var(--border-threshold)) * 10);
  
  background: hsl(var(--hue), calc(var(--s) * 1%), calc(var(--l) * 1%));
  color: hsl(0, 0%, var(--switch));
  border:.2em solid hsla(var(--hue), calc(var(--s) * 1%), var(--border-light), var(--border-alpha));
}

.secondary {
  --hue: calc(var(--h) + 60);
}
View Compiled
const inputs = document.querySelectorAll("input");

const color = [...inputs].map((input, index) => {
  input.addEventListener("change", function (e) {
    handleUpdate(e, index);
  });
  return input.value;
});

function handleUpdate(e, index) {
  color[index] = e.target.value;

  document.documentElement.style.setProperty(
    `--${e.target.id}`,
    `${e.target.value}`
  );
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.