Set Child Width Relative to Its Parents Height in Pure CSS

Set child width relative to its parents height in pure css

Just assign your parent's height property value to a css variable and then use calc() to assign your child element's width to a value that is 10% of your parent's height.

Check and run the Code Snippet below for a practical example of what I have described above:

.parent {
   position: relative;
   --parentHeight: 300px;
   height: var(--parentHeight);
   width: 600px;
   background-color: red;
 }
 .parent .resized {
   height: 100px;
 }

 .child {
   position: absolute;
   height: 20%;
   width: calc(var(--parentHeight) / 10);
   background-color: green;
 }

<div class="parent">
  <div class="child"></div>
</div>

Set child's width to the height of the parent in pure CSS

Based on this specific demo, you could use viewport relative units and it will work as expected.

Use width: 80vh in this case - updated example. You can find browser support here.

Since #parent-div has a height of 80% of the viewport, you can use 80vh to set #child-div's width to the same height. This clearly won't work if #parent-div doesn't have a height of 80% of the viewport, though.

As an alternative, you would have to avoid rotating the child element, and just rotate the parent element and give the child element a height of 100%.

How can I expand floated child div's height to parent's height?

For the parent element, add the following properties:

.parent {
    overflow: hidden;
    position: relative;
    width: 100%;
}

then for .child-right these:

.child-right {
    background:green;
    height: 100%;
    width: 50%;
    position: absolute;
    right: 0;
    top: 0;
}

Find more detailed results with CSS examples here and more information about equal height columns here.

Relative parent DIV to inherit the width of absolute child DIV

The short answer is that what you are asking basically can't be done with pure CSS / HTML. (at least without tables) You'd need Javascript that would read #child's width/height and then do the calculation you want to do (I don't know) and set a new height/width to #parent.

Otherwise, if you mean that you want #child's height/width to change according to its content, of course this is native CSS, just set it's height/width to auto and then start adding text inside it you'll see it will start growing to fit your content inside.

As the #child is positioned absolute, then it is taken OUT of the normal flow of the document, therefore it will not affect the #parent.

Is there a pure CSS way to make a child element fit into parent with stepped (width) values

CSS grid can do it:

.wrapper {
  display: grid;
  grid-template-columns: repeat(auto-fill, 50px); /* your step */
  justify-content: center; /* remove if you want left align */
}

h1 {
  grid-column: 1/-1; /* take all the possible columns */
  
  /* to demoonstrate the repetition */
  padding-bottom: 80px;
  background: url(https://picsum.photos/id/1069/50/50) bottom left repeat-x;
}

<div class="wrapper">
  <h1>a title</h1>
</div>

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