inset-block-start

writing-mode: horizontal-tb;

writing-mode: vertical-rl;

writing-mode: horizontal-tb;
direction: rtl;

writing-mode: vertical-lr;

<section id="default-example">
  <div class="example-container" id="example-element">
    <div id="abspos">
      I am absolutely positioned with inset-block-start: 50px
    </div>
    <p>
      As much mud in the streets as if the waters had but newly retired from the
      face of the earth, and it would not be wonderful to meet a Megalosaurus,
      forty feet long or so, waddling like an elephantine lizard up Holborn
      Hill.
    </p>
  </div>
</section>

#example-element {
  border: 0.75em solid;
  padding: 0.75em;
  position: relative;
  width: 100%;
  min-height: 200px;
  unicode-bidi: bidi-override;
}
#abspos {
  background-color: yellow;
  color: black;
  border: 3px solid red;
  position: absolute;
  inset-block-start: 50px;
  inline-size: 140px;
}

/* <length> values */
inset-block-start: 3px;
inset-block-start: 2.4em;
inset-block-start: anchor(end);
inset-block-start: calc(anchor-size(--my-anchor height, 70px) * 2);
/* <percentage>s of the width or height of the containing block */
inset-block-start: 10%;
/* Keyword value */
inset-block-start: auto;
/* Global values */
inset-block-start: inherit;
inset-block-start: initial;
inset-block-start: revert;
inset-block-start: revert-layer;
inset-block-start: unset;

<div>
  <p class="exampleText">Example text</p>
</div>

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}
.exampleText {
  writing-mode: vertical-lr;
  position: relative;
  inset-block-start: 20px;
  background-color: #c8c800;
}