<div class="controls"> 
  <label for="writingmode">writing-mode:</label>
  <select id="writingmode">
    <option value="horizontal-tb">horizontal-tb</option>
    <option value="vertical-lr">vertical-lr</option>
    <option value="vertical-rl">vertical-rl</option>
  </select>
</div>

<div id="wrapper">
  <div class="box" id="typical">
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
  </div>
  <div class="box" id="logical">
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
  </div>
</div>
:root {
  --bgcolor: #fff;
  --color: #333;
}
/* Dark mode */
@media screen and (prefers-color-scheme: dark) {
  :root {
    --color: #fff;
    --bgcolor: #101010;
  }
  a:link, a:visited {
    color: #0ff;
  }
}
body {
   color: #fff;
   background-color: #101010;
   width: 100vw;
   min-height: 100vh;
   display: flex;
   flex-direction: column;
   align-items: center;
   padding: 6vh;
    margin: 0;
    box-sizing: border-box;
 }

.controls {
  margin: 0;
  padding: .5em 2em 1em 2em;
  border-bottom: 1px solid #666;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: var(--bgcolor);
  color: var(--color)
}
.controls select {
  margin-right: 1.25rem;
  color: #2f4f4f;
  font-size: 1.2rem;
}

#wrapper {
  padding-top: 40px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 80vw;
  flex: 1;
}

.box {
  // width: 30vw;
  // border: 1px solid #ccc;
  // margin: 2vh;
  // padding: 3vh;
  
  border-radius: 4px;
  display: flex;
  flex-direction: column;
  
  position: relative;
  
  &::before,
  &::after {
    content: '';
    position: absolute;
  }
}

.line {
  background-color: rgba(#f36, .36);
  border-radius: 2px;
}

#typical {
  width: 30vw;
  border: 1px solid #ccc;
  margin: 2vh;
  padding: 3vh;
  
  &::before {
    content: 'width(x)';
    left: 50%;
    bottom: calc(100% + 2vh);
    transform: translate(-50%, 0);
  }
  
  &::after {
    content: 'height(y)';
    top: 50%;
    right: calc(100% + 2vh);
    transform: translate(0, -50%) rotate(90deg);
  }
  
  .line {
    width: 100%;
    min-height: 4vh;
    margin: 1vh;

    &:nth-child(2) {
      width: calc(100% - 2vw);
    }

     &:nth-child(3) {
      width: calc(100% - 4vw);
    }

    &:nth-child(4) {
      width: calc(100% - 6vw);
    }

    &:nth-child(5) {
      width: calc(100% - 8vw);
    }

    &:nth-child(6) {
      width: calc(100% - 10vw);
    }
  }
}

#logical {
  inline-size: 30vw;
  border-inline:  1px solid #ccc;
  border-block:  1px solid #ccc;
  padding-inline: 3vh;
  padding-block: 3vh;
  margin-inline: 2vh;
  margin-block: 2vh;
  
  &::before {
    content: 'inline-size(inline)';
    inset-inline-start: 50%;
    inset-block-end: calc(100% + 2vh);
    transform: translate(-50%, 0);
  }
  
  &::after {
    content: 'block-size(block)';
    inset-block-start: 50%;
    inset-inline-start: calc(100% - 4vh);
    transform: translate(0, -50%) rotate(90deg);
    white-space: nowrap;
  }
  
  .line {
    inline-size: 100%;
    min-block-size: 4vh;
    margin-inline: 1vh;
    margin-block: 1vh;

    &:nth-child(2) {
      inline-size: calc(100% - 2vw);
    }

     &:nth-child(3) {
      inline-size: calc(100% - 4vw);
    }

    &:nth-child(4) {
      inline-size: calc(100% - 6vw);
    }

    &:nth-child(5) {
      inline-size: calc(100% - 8vw);
    }

    &:nth-child(6) {
      inline-size: calc(100% - 10vw);
    }
  }
}
View Compiled
const writingModeSelector = document.getElementById('writingmode');
const wrapper = document.getElementById('wrapper')

writingModeSelector.addEventListener('change', (e) => {
  console.log('====> writing-mode:', e.target.value)
  wrapper.style.writingMode=e.target.value
})
View Compiled

External CSS

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External JavaScript

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