<header>
  <div class="control">
    <label for="justify-content">justify-content:</label>
    <select name="justify-content" id="justify-content">
      <option value="normal">normal</option>
      <optgroup label="content-distribution">
        <option value="space-between">space-between</option>
        <option value="space-around">space-around</option>
        <option value="space-evenly">space-evenly</option>
        <option value="stretch">stretch</option>
      </optgroup>
      <optgroup label="overflow-position">
        <option value="unsafe">unsafe</option>
        <option value="safe">safe</option>
      </optgroup>
      <optgroup label="content-position">
        <option value="center">center</option>
        <option value="start">start</option>
        <option value="end">end</option>
        <option value="flex-start">flex-start</option>
        <option value="flex-end">flex-end</option>
      </optgroup>
      <option value="left">left</option>
      <option value="right">right</option>
    </select>
  </div>
  <div class="control">
    <label for="align-content">align-content:</label>
    <select name="align-content" id="align-content">
      <option value="normal">normal</option>
      <optgroup label="baseline-position">
        <option value="baseline">baseline</option>
        <option value="first baseline">first baseline</option>
        <option value="last baseline">last baseline</option>
      </optgroup>
      <optgroup label="content-distribution">
        <option value="space-between">space-between</option>
        <option value="space-around">space-around</option>
        <option value="space-evenly">space-evenly</option>
        <option value="stretch">stretch</option>
      </optgroup>
      <optgroup label="overflow-position">
        <option value="unsafe">unsafe</option>
        <option value="safe">safe</option>
      </optgroup>
      <optgroup label="content-position">
        <option value="center">center</option>
        <option value="start">start</option>
        <option value="end">end</option>
        <option value="flex-start">flex-start</option>
        <option value="flex-end">flex-end</option>
      </optgroup>
    </select>
  </div>
</header>
<div class="container flex-container">
  <div class="item" style="--color:#F44336;"></div>
  <div class="item" style="--color:#E91E63;"></div>
  <div class="item" style="--color:#9C27B0;"></div>
  <div class="item" style="--color:#3F51B5;"></div>
  <div class="item" style="--color:#2196F3;"></div>
  <div class="item" style="--color:#009688;"></div>
  <div class="item" style="--color:#CDDC39;"></div>
  <div class="item" style="--color:#FFC107;"></div>
  <div class="item" style="--color:#607D8B;"></div>
  <div class="item" style="--color:#3E989B;"></div>
</div>

<div class="container flex-container direction-column">
  <div class="item" style="--color:#F44336;"></div>
  <div class="item" style="--color:#E91E63;"></div>
  <div class="item" style="--color:#9C27B0;"></div>
  <div class="item" style="--color:#3F51B5;"></div>
  <div class="item" style="--color:#2196F3;"></div>
  <div class="item" style="--color:#009688;"></div>
  <div class="item" style="--color:#CDDC39;"></div>
  <div class="item" style="--color:#FFC107;"></div>
  <div class="item" style="--color:#607D8B;"></div>
  <div class="item" style="--color:#3E989B;"></div>
</div>

<div class="container grid">
  <div class="item" style="--color:#F44336;"></div>
  <div class="item" style="--color:#E91E63;"></div>
  <div class="item" style="--color:#9C27B0;"></div>
  <div class="item" style="--color:#3F51B5;"></div>
  <div class="item" style="--color:#2196F3;"></div>
  <div class="item" style="--color:#009688;"></div>
  <div class="item" style="--color:#CDDC39;"></div>
  <div class="item" style="--color:#FFC107;"></div>
  <div class="item" style="--color:#607D8B;"></div>
  <div class="item" style="--color:#3E989B;"></div>
</div>

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

* {
  box-sizing: border-box;
}

body {
  width: 100vw;
  min-height: 100vh;
  counter-reset: section;
  font-family: "Exo", Arial, sans-serif;
  font-size: 20px;
  font-weight: 600;
  padding: 10px;
  box-sizing: border-box;
  background-color: #222;
  color: #777;

  display: grid;

  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: 100px 1fr;
  gap: 10px;
}

header {
  grid-column: span 3;
  display: flex;
  justify-content: center;
  align-items: center;
  color: #fff;
}

header label {
  margin: 0 5px;
}

.container {
  border: 1px dotted #fff;
  counter-reset: section;
  max-height: calc(100vh - 160px);
  position: relative;
}

.item {
  border: 1px solid #000;
  border-radius: 10px;
  font-size: 1em;
  background-color: #3e989b;
  background-color: var(--color);
  color: white;
  display: grid;
}

.item::before {
  counter-increment: section;
  content: counter(section);
  justify-self: center;
  align-self: center;
  color: white;
}

.flex-container {
  display: flex;
  flex-wrap: wrap;
  padding: 10px;
  gap: 10px;
}

.flex-container .item {
  min-width: 70px;
  min-height: 70px;
}

.direction-column {
  flex-direction: column;
}

.grid {
  display: grid;
  grid-template-columns: repeat(5, 70px);
  grid-template-rows: repeat(3, 70px);
  padding: 10px;
  gap: 10px;
  height: 100%;
  width: 100%;
}

.flex-container::before {
  content: "display: flex; flex-wrap: wrap";
  position: absolute;
  left: 0;
  bottom: calc(100% + 5px);
  color: #fff;
  font-size: 12px;
}

.flex-container.direction-column::before {
  content: "display: flex; flex-wrap: wrap; flex-direction: column";
}

.grid.container::before {
  content: "display: gird;grid-template-columns: repeat(5, 70px); grid-template-rows: repeat(3, 70px)";
  position: absolute;
  left: 0;
  bottom: calc(100% + 5px);
  color: #fff;
  font-size: 12px;
}

:root {
  --justify-content: normal;
  --align-content: normal;
}

.container {
  justify-content: var(--justify-content);
  align-content: var(--align-content);
}

const rootElement = document.documentElement;

const selects = document.querySelectorAll("select");

selects.forEach((select) =>
  select.addEventListener("change", (e) => {
    rootElement.style.setProperty(`--${e.target.id}`, e.target.value);
  })
);