CSS Box Sizing

iframe {
  display: block;
  border: 1px dashed black;
}

<label id="wf" for="w">width:165</label>
<input id="w" name="w" type="range" min="100" max="250" step="5" value="165" />
<label id="hf" for="w">height:165</label>
<input id="h" name="h" type="range" min="100" max="250" step="5" value="165" />
<label id="ratio">aspect-ratio: 165/165 = 1</label>

<iframe
  id="outer"
  srcdoc="<style> @media (min-aspect-ratio: 8/5) { div { background: #9999ff; } } @media (max-aspect-ratio: 3/2) { div { background: #99ff99; } } @media (aspect-ratio: 1/1) { div { background: #ff9999; } }</style><div id='inner'> Watch this element as you resize iframe viewport's width and height.</div>">
</iframe>

outer.style.width = outer.style.height = "165px";

const updateRatio = () => {
  ratio.textContent = `aspect-ratio: ${w.value}/${h.value} = ${(w.value / h.value).toFixed(2)}`;
};

w.onchange = w.oninput = () => {
  outer.style.width = `${w.value}px`;
  wf.textContent = `width: ${w.value}`;
  updateRatio();
};

h.onchange = h.oninput = () => {
  outer.style.height = `${h.value}px`;
  hf.textContent = `height: ${h.value}`;
  updateRatio();
};

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the block-size.
  </div>
</section>

#example-element-parent {
  width: 220px;
  height: 200px;
  border: solid 10px #ffc129;
  margin: 0.8em;
}

#example-element {
  height: 60px;
  margin: 2em auto;
  background-color: rgb(81 81 81 / 0.6);
}

#example-element > p {
  margin: 0;
}

<section id="default-example">
  <div id="example-element-parent">
    <p>Parent container</p>
    <div class="transition-all" id="example-element">
      <p>Child container</p>
    </div>
  </div>
</section>

#example-element {
  width: 100%;
  columns: auto;
  text-align: left;
}

<section id="default-example">
  <p id="example-element">
    London. Michaelmas term lately over, and the Lord Chancellor sitting in
    Lincoln's Inn Hall. Implacable November weather. 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>
</section>

#contained_element {
  border: 2px solid green;
  inline-size: 151px;
  content-visibility: auto;
  contain-intrinsic-inline-size: 152px;
  contain-intrinsic-block-size: 52px;
}
.child_element {
  border: 1px solid red;
  background: blue;
  block-size: 50px;
  inline-size: 150px;
}

<div id="contained_element">
  <div class="child_element"></div>
</div>

#contained_element {
  border: 2px solid green;
  width: 151px;
  content-visibility: auto;
  contain-intrinsic-width: 152px;
  contain-intrinsic-height: 52px;
}
.child_element {
  border: 1px solid red;
  background: blue;
  height: 50px;
  width: 150px;
}

<div id="contained_element">
  <div class="child_element"></div>
</div>

#contained_element {
  border: 2px solid green;
  inline-size: 151px;
  content-visibility: auto;
  contain-intrinsic-inline-size: 152px;
  contain-intrinsic-block-size: 52px;
}
.child_element {
  border: 1px solid red;
  background: blue;
  block-size: 50px;
  inline-size: 150px;
}

<div id="contained_element">
  <div class="child_element"></div>
</div>

div,
p {
  padding: 1rem;
  margin-bottom: 1rem;
  font-size: 2rem;
  font-family: sans-serif;
}

code {
  background-color: lightgray;
  padding: 0.25rem;
  border-radius: 0.25rem;
}

#container {
  width: 90%;
  height: 80%;
}

.auto-length,
.auto-length.none {
  display: none;
}

#auto-length-note,
#auto-none-note {
  display: block;
  padding: 0;
}

#auto-length-note p,
#auto-none-note p {
  padding: 0.5rem;
  width: 100%;
  height: max-content;
  font-size: 1rem;
  line-height: 1.5rem;
  background-color: tomato;
}

@supports (contain-intrinsic-size: auto none) {
  .auto-length.none {
    display: block;
  }
  #auto-none-note {
    display: none;
  }
}
@supports (contain-intrinsic-size: auto 500px) {
  .auto-length {
    display: block;
  }
  #auto-length-note {
    display: none;
  }
}

p {
  height: 500px;
  width: 500px;
  border: 4px dotted;
  background: lightblue;
}

.auto-length {
  content-visibility: auto;
  contain-intrinsic-size: auto 500px;
  background-color: linen;
  outline: 4px dotted blue;
}

.large-intrinsic-size {
  /* Setting an inaccurate intrinsic size for the element */
  contain-intrinsic-size: auto 5000px;
  background-color: lightgray;
  outline: 4px dotted red;
}

.small {
  /* This element is a lot smaller than expected */
  height: 100px;
  width: 100px;
}

.none {
  background-color: papayawhip;
  contain-intrinsic-size: auto none;
  outline: 4px dotted red;
}

<div id="container">
  <div id="auto-length-note">
    <p>
      Your browser does not support
      <code>contain-intrinsic-size: auto &lt;length&gt;</code>.
    </p>
  </div>
  <div class="auto-length">
    <p>Item one</p>
  </div>
  <div class="auto-length">
    <p>Item two</p>
  </div>
  <div class="auto-length large-intrinsic-size">
    <p class="small">Item three</p>
  </div>
  <div class="auto-length large-intrinsic-size">
    <p class="small">Item four</p>
  </div>
  <div id="auto-none-note">
    <p>
      Your browser does not support
      <code>contain-intrinsic-size: auto none</code>.
    </p>
  </div>
  <div class="auto-length none">
    <p>Item five</p>
  </div>
  <div class="auto-length none">
    <p>Item six</p>
  </div>
</div>

#contained_element {
  border: 2px solid green;
  width: 151px;
  content-visibility: auto;
  contain-intrinsic-width: 152px;
  contain-intrinsic-height: 52px;
}
.child_element {
  border: 1px solid red;
  background: blue;
  height: 50px;
  width: 150px;
}

<div id="contained_element">
  <div class="child_element"></div>
</div>

iframe {
  frame-sizing: content-block-size;
  border: 2px solid gray;
}

<h1>Responsive iframes — basic example</h1>

<iframe src="frame.html"></iframe>

<head>
  ...

  <meta name="responsive-embedded-sizing" />

  ...
</head>
<body>
  <h1>This is my frame</h1>
  <p>This is the content of my discontent.</p>
  <p>This is some more content.</p>
</body>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the inline-size.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the maximum block size. <br />This will
    limit the size in the block dimension, potentially causing an overflow.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the maximum height. <br />This will limit
    how tall the box can be, potentially causing an overflow.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the max-inline-size.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    Change the maximum width.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the minimum block size. <br />If there is
    more content than the minimum the box will grow in the block dimension as
    needed by the content.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the minimum height. <br />If there is
    more content than the minimum the box will grow to the height needed by the
    content.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">Change min-inline-size</div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    Change the minimum width.
  </div>
</section>