Row like div inside a flex environment with a rotated heading at the beginning

Question

Goal

Eventually I want to get something like this (forget about the white border around this is due to the clipping):

Constraints

This elements must sit within the following markup which I cannot change easily:

<div style="position:absolute;top:15px;right:15px;bottom:15px;left:15px">
  <div style="display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;width:100%;height:100%;">
     <div style="position:relative;-webkit-flex:1;-ms-flex:1;flex:1;width:100%;height:100%;">
        <div style="position:absolute;top:0;left:0;right:0;bottom:0;">
          <!-- place elements here -->
        </div>
     </div>
  </div>
</div>

What I tried

<div class="split-container">
  <div class="split-heading">
    <h3>Heading</h3>
  </div>
  <div class="split-content">
    <p>Content</p>
  </div>
</div>

.split-container {
  display: flex;
  height: 100%;
}

.split-heading {
  background-color: rgb(198,89,17);
  color: #fff;
  padding: 0 5px; /* Add padding to the sides */
}

.split-heading > h3 {
  transform: rotate(-90deg);
  transform-origin: bottom right;
}

.split-content {
  flex-grow: 100;
  background-color: rgb(244,176,132);
  color: #fff;
}

Result

https://codepen.io/thothal/pen/qBwxEKO

Issues

• The heading div should only take the needed space (it is too broad right now)
• The heading should vertically and horizontally centered
• The content should be vertically centered

Answer 1

Solution:

• You can use the css writing-mode property to display the text vertically, then rotate it 180 degrees, to flip it. Then set margin to 0px (because <h3> tags have already a margin).
• Add a display: flex, align-items: center to the split-heading class to center it.
• Add a display: flex, align-items: center to the split-content class to center it.

.split-container {
  display: flex;
}

.split-heading {
  background-color: rgb(198,89,17);
  color: #fff;
  padding: 0 5px; /* Add padding to the sides */
  display: flex;
  align-items: center;
}

.split-heading > h3 {
  transform: rotate(180deg);
  writing-mode: vertical-lr;
  margin: 0px;
}

.split-content {
  flex-grow: 100;
  background-color: rgb(244,176,132);
  color: #fff;
  display: flex;
  align-items: center;
}

<div style="position:absolute;top:15px;right:15px;bottom:15px;left:15px">
  <div style="display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;width:100%;height:100%;">
     <div style="position:relative;-webkit-flex:1;-ms-flex:1;flex:1;width:100%;height:100%;">
        <div style="position:absolute;top:0;left:0;right:0;bottom:0;">
          <div class="split-container">
            <div class="split-heading">
              <h3>Heading</h3>
            </div>
            <div class="split-content">
              <p>Content</p>
            </div>
          </div>
        </div>
     </div>
  </div>
</div>