<div class="select">
  <label for="box-sizing">box-sizing:</label>
  <select name="box-sizing" id="box-sizing">
    <option value="border-box">border-box</option>
    <option value="content-box">content-box</option>
  </select>
</div>
<div class="wrapper">
  <div class="box">
    <div class="width" contenteditable>我是一个块元素</div>
  </div>
</div>

<div class="form">
  <div class="control">
    <label for="margin-left">margin-left:</label>
    <div class="rang padding-left">
      <span class="min">0</span>
      <input type="range" id="margin-left" value="5" min="0" max="30" step="1" />
      <span class="max">30</span>
      <output class="output" for="margin-left">5px</output>
    </div>
  </div>

  <div class="control">
    <label for="border-left">border-left:</label>
    <div class="rang border-left">
      <span class="min">0</span>
      <input type="range" id="border-left" value="5" min="0" max="20" step="1" />
      <span class="max">20</span>
      <output class="output" for="border-left">5px</output>
    </div>
  </div>

  <div class="control">
    <label for="padding-left">padding-left:</label>
    <div class="rang padding-left">
      <span class="min">0</span>
      <input type="range" id="padding-left" value="5" min="0" max="30" step="1" />
      <span class="max">30</span>
      <output class="output" for="padding-left">5px</output>
    </div>
  </div>

  <div class="control">
    <label for="padding-right">padding-right:</label>
    <div class="rang padding-right">
      <span class="min">0</span>
      <input type="range" id="padding-right" value="5" min="0" max="30" step="1" />
      <span class="max">30</span>
      <output class="output" for="padding-right">5px</output>
    </div>
  </div>

  <div class="control">
    <label for="border-right">border-right:</label>
    <div class="rang border-right">
      <span class="min">0</span>
      <input type="range" id="border-right" value="5" min="0" max="20" step="1" />
      <span class="max">20</span>
      <output class="output" for="border-right">5px</output>
    </div>
  </div>

  <div class="control">
    <label for="margin-right">margin-right:</label>
    <div class="rang margin-right">
      <span class="min">0</span>
      <input type="range" id="margin-right" value="5" min="0" max="30" step="1" />
      <span class="max">30</span>
      <output class="output" for="margin-right">5px</output>
    </div>
  </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: flex;
  justify-content: space-between;
  flex-wrap: wrap;
}

label {
  display: block;
  margin-bottom: 5px;
}

.control {
  margin: 20px 10px;
  flex: 1;
}


.rang {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 5px;
}
.min {
  text-align: right;
 }

.output {
  grid-column: 2 / 3;
  grid-row: 2 / 3;
  text-align: center;
  border: 1px dashed currentColor;
  border-radius: 5px;
  padding: 6px 0;
  position: relative;
}

:root {
  --margin-left: 5px;
  --border-left: 5px;
  --padding-left: 5px;
  --padding-right: 5px;
  --border-right: 5px;
  --margin-right: 5px;
  --box-sizing: border-box;
}

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

.box {
  width: 30vw;
  min-height: 30vh;
  border: 1px dashed #fff;
  border-radius: 5px;
}

.width {
  min-height: 200px;
  text-align: center;
  background-color: #f36;
  border-radius: 5px 5px 0 0;
  border: 5px solid #03a9f4;
  background-image:linear-gradient(to bottom, #9c27b0, #9c27b0), linear-gradient(to right, #ffeb3b, #ffeb3b);
  background-origin:content-box, padding-box;
  background-clip: content-box, padding-box;

  margin: 5px var(--margin-right) 5px var(--margin-left);
  border-width: 0 var(--border-right) 0 var(--border-left);
  padding: 0 var(--padding-right) 0 var(--padding-left);
  box-sizing: var(--box-sizing);
}

.select {
  margin-bottom: 10px;
}
.select label {
  display: inline-block;
}

.code {
  position: absolute;
  left: 10px;
  right: 10px;
  bottom: 10px;
  white-space: nowrap;
  text-align: center;
}

const inputs = document.querySelectorAll("input");
const select = document.querySelector("#box-sizing");
const code = document.querySelector(".code");
const boxWidth = document.querySelector(".box");

inputs.forEach((input) => input.addEventListener("change", handleUpdate));

function handleUpdate(e) {
  this.parentNode.querySelector("output").textContent = `${this.value}px`;
  document.documentElement.style.setProperty(`--${this.id}`, `${this.value}px`);
}

select.addEventListener("change", (e) => {
  document.documentElement.style.setProperty("--box-sizing", e.target.value);
});