CodePen Embed - place auto in flexbox or grid layout

<div class="c_checkbox">
  <div class="control">
    <label for="c_justify-self">
      <input type="checkbox" id="c_justify-self" class="checkbox" name="c_justify-self" />justify-self: auto
    </label>
  </div>
  <div class="control">
    <label for="c_align-self">
      <input type="checkbox" id="c_align-self" class="checkbox" name="c_align-self" />align-self: auto
    </label>
  </div>
</div>
<div class="wrapper">
  <div class="box">
    <div class="element" contenteditable>place auto in flexbox or grid layout</div>
  </div>
</div>

<div class="form">
  <div class="control">
    <label for="display">display:</label>
    <select name="display" id="display">
      <option value="flex">flex</option>
      <option value="inline-flex">inline-flex</option>
      <option value="grid">grid</option>
      <option value="inline-grid">inline-grid</option>
    </select>
  </div>
  <div class="control">
    <label for="justify-content">justify-content:</label>
    <select name="justify-content" id="justify-content">
      <option value="baseline">baseline</option>
      <option value="center">center</option>
      <option value="end">end</option>
      <option value="flex-end">flex-end</option>
      <option value="flex-start">flex-start</option>
      <option value="left">left</option>
      <option value="normal" selected>normal</option>
      <option value="right">right</option>
      <option value="safe">safe</option>
      <option value="space-around">space-around</option>
      <option value="space-between">space-between</option>
      <option value="space-evenly">space-evenly</option>
      <option value="start">start</option>
      <option value="stretch">stretch</option>
      <option value="unsafe">unsafe</option>
    </select>
  </div>
  <div class="control">
    <label for="align-items">align-items:</label>
    <select name="align-items" id="align-items">
      <option value="baseline">baseline</option>
      <option value="center">center</option>
      <option value="end">end</option>
      <option value="flex-end">flex-end</option>
      <option value="flex-start">flex-start</option>
      <option value="left">left</option>
      <option value="normal" selected>normal</option>
      <option value="right">right</option>
      <option value="safe">safe</option>
      <option value="space-around">space-around</option>
      <option value="space-between">space-between</option>
      <option value="space-evenly">space-evenly</option>
      <option value="start">start</option>
      <option value="stretch">stretch</option>
      <option value="unsafe">unsafe</option>
    </select>
  </div>
  <div class="control">
    <label for="align-content">align-content:</label>
    <select name="align-content" id="align-content">
      <option value="baseline">baseline</option>
      <option value="center">center</option>
      <option value="end">end</option>
      <option value="flex-end">flex-end</option>
      <option value="flex-start">flex-start</option>
      <option value="left">left</option>
      <option value="normal" selected>normal</option>
      <option value="right">right</option>
      <option value="safe">safe</option>
      <option value="space-around">space-around</option>
      <option value="space-between">space-between</option>
      <option value="space-evenly">space-evenly</option>
      <option value="start">start</option>
      <option value="stretch">stretch</option>
      <option value="unsafe">unsafe</option>
    </select>
  </div>
  <div class="control">
    <label for="justify-self">justify-self:</label>
    <select name="justify-self" id="justify-self">
      <option value="baseline">baseline</option>
      <option value="center">center</option>
      <option value="end">end</option>
      <option value="flex-end">flex-end</option>
      <option value="flex-start">flex-start</option>
      <option value="left">left</option>
      <option value="normal" selected>normal</option>
      <option value="right">right</option>
      <option value="safe">safe</option>
      <option value="space-around">space-around</option>
      <option value="space-between">space-between</option>
      <option value="space-evenly">space-evenly</option>
      <option value="start">start</option>
      <option value="stretch">stretch</option>
      <option value="unsafe">unsafe</option>
    </select>
  </div>

  <div class="control">
    <label for="align-self">align-self:</label>
    <select name="align-self" id="align-self">
      <option value="baseline">baseline</option>
      <option value="center">center</option>
      <option value="end">end</option>
      <option value="flex-end">flex-end</option>
      <option value="flex-start">flex-start</option>
      <option value="left">left</option>
      <option value="normal" selected>normal</option>
      <option value="right">right</option>
      <option value="safe">safe</option>
      <option value="space-around">space-around</option>
      <option value="space-between">space-between</option>
      <option value="space-evenly">space-evenly</option>
      <option value="start">start</option>
      <option value="stretch">stretch</option>
      <option value="unsafe">unsafe</option>
    </select>
  </div>

</div>

@import url("https://fonts.googleapis.com/css?family=Gochi+Hand");

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

body {
  margin: 0;
  padding: 0;
  background-color: #291642;
  font-family: "Gochi Hand", sans-serif;
  color: #fff;
  font-size: 130%;
  letter-spacing: 0.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  width: 100vw;
  min-height: 100vh;
  padding: 10px;
}

.form {
  padding: 20px;
  width: 100%;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
}

.c_checkbox {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 5px;
}

.c_checkbox label {
  margin-right: 5px;
}

.c_checkbox .control {
  display: flex;
}

.c_checkbox .control:nth-child(1) {
  margin-left: auto;
}

.c_checkbox .control:nth-child(2) {
  margin-right: auto;
}

.control {
  margin: 20px 10px;
  display: grid;
  grid-template-columns: 0.8fr 1fr;
  gap: 5px;
  align-items: center;
}

.control label {
  white-space: nowrap;
  margin: 0 0 0 auto;
}

.control:nth-child(1),
.control:nth-child(4) {
  margin-left: auto;
}
.control:nth-child(3n) {
  margin-right: auto;
}

.control:nth-child(2),
.control:nth-child(5) {
  margin-right: auto;
  margin-left: auto;
}

.checkbox {
  margin: 0 5px 0 0;
}

.wrapper {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}

:root {
  --display: flex;
  --justify-content: normal;
  --align-content: normal;
  --align-items: normal;
  --justify-self: normal;
  --align-self: normal;
}
.box {
  width: 60vw;
  height: 50vh;
  border-radius: 5px;
  padding: 5px;
  border: 1px dashed #fff;
  position: relative;
  display: var(--display);
  justify-content: var(--justify-content);
  align-items: var(--align-items);
  align-content: var(--align-content);
}

.element {
  text-align: center;
  background-color: #f36;
  padding: 5vh;
  border-radius: 5px;
  justify-self: var(--justify-self);
  align-self: var(--align-self);
}

View Compiled

const checkboxs = document.querySelectorAll(".checkbox");
const elemment = document.querySelector(".element");
const selects = document.querySelectorAll("select");

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

checkboxs.forEach((checkbox) =>
  checkbox.addEventListener("change", (e) => {
    if (e.target.checked) {
      if (e.target.name === "c_justify-self") {
        document.documentElement.style.setProperty(`--justify-self`, `auto`);

        document.querySelector("#justify-self").disabled = true;
      }

      if (e.target.name === "c_align-self") {
        document.documentElement.style.setProperty(`--align-self`, `auto`);
        document.querySelector("#align-self").disabled = true;
      }
    } else {
      if (e.target.name === "c_justify-self") {
        document.documentElement.style.setProperty(`--justify-self`, `normal`);
        document.querySelector("#justify-self").disabled = false;
      }

      if (e.target.name === "c_align-self") {
        document.documentElement.style.setProperty(`--align-self`, `normal`);
        document.querySelector("#align-self").disabled = true;
      }
    }
  })
);

View Compiled

This Pen is owned by 大漠 on CodePen.

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