<div class="demo-container">
  <h2>Dynamic Color Spectrum</h2>
  <p>The <code>background-color</code> is set with <code>oklch()</code>, where the hue is calculated based on the item's index and the total sibling count.</p>
  <div class="controls">
    <button id="add-item">Add Color</button>
    <button id="remove-item">Remove Color</button>
  </div>
  <div class="spectrum-list">
    <div class="spectrum-item"></div>
    <div class="spectrum-item"></div>
    <div class="spectrum-item"></div>
    <div class="spectrum-item"></div>
    <div class="spectrum-item"></div>
  </div>
</div>

@import url("https://fonts.googleapis.com/css2?family=Poppins:wght@400;600;700&display=swap");

.spectrum-list {
  display: flex;
  height: 80px;
  background: #34495e;
  border-radius: 10px;
  padding: 1rem;
  gap: 1rem;
}

.spectrum-item {
  --start-hue: 180; /* Teal */
  --hue-range: 120; /* Range from Teal to Magenta */
  flex-grow: 1;
  border-radius: 6px;

  /* distribute a range of hues across all items using sibling-count and index */
  background-color: oklch(
    65% 0.35
      calc(
        var(--start-hue) + (var(--hue-range) / (sibling-count() - 1)) *
          (sibling-index() - 1)
      )
  );

  transition: background-color 0.4s ease;
}

@layer basestyles {
  :root {
    --bg-color: #f0f2f5;
    --text-color: #333;
    --accent-grad: linear-gradient(160deg, #ff7e9b, #8a7eff);
  }

  body {
    font-family: "Poppins", sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    padding: 3rem 1rem;
    display: grid;
    gap: 3.5rem;
    justify-items: center;
  }

  .demo-container {
    width: 100%;
    max-width: 650px;
    text-align: center;
  }

  h2 {
    margin-bottom: 0.5rem;
  }

  p {
    margin-top: 0;
    margin-bottom: 1.5rem;
    color: #666;
    max-width: 500px;
    margin-left: auto;
    margin-right: auto;
  }
  code {
    background-color: #e2e5e9;
    padding: 0.2em 0.4em;
    border-radius: 4px;
    font-size: 0.9em;
  }

  button {
    font-family: inherit;
    font-size: 1rem;
    font-weight: 600;
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 8px;
    background-image: var(--accent-grad);
    color: white;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    margin: 0 0.5rem 1.5rem;
    &:hover {
      transform: translateY(-2px);
      box-shadow: 0 6px B20px rgba(138, 126, 255, 0.4);
    }
  }
}

const spectrumList = document.querySelector(".spectrum-list");
const addItemBtn = document.getElementById("add-item");
const removeItemBtn = document.getElementById("remove-item");

addItemBtn.addEventListener("click", () => {
  if (spectrumList.children.length < 12) {
    const newItem = document.createElement("div");
    newItem.classList.add("spectrum-item");
    spectrumList.appendChild(newItem);
  }
});

removeItemBtn.addEventListener("click", () => {
  if (spectrumList.children.length > 2) {
    spectrumList.removeChild(spectrumList.lastElementChild);
  }
});