css width same as height

问题

I would like to do the next trick in my css file so that (height = width) without setting pixels. I want to do this so whatever the resolution of the browser is, to have same values on these two dimensions.

#test{
    height: 100%;
    width: (same as height);
}

I prefer to do it with css and not javascript.

Thank you in advance.

回答1:

The only CSS way of doing this at the moment (AFAIK) is using viewport relates values (vh / vw )

Support is not great at the moment: http://caniuse.com/viewport-units but here is a quick demo

JSFiddle

CSS

.box {
    background-color: #00f;
    width: 50vw;
    height:50vw;
}

The box is responsive but will always remain square.

Pure % values will not work as height:100% does not equal width:100% as they refer to different things being the relevant dimensions of the parent.

回答2:

Another options is to make aspect ratio using img element behavior

Here i use svg image and inline it with data url to make it simpler

To describe desired aspect ratio you can use viewBox svg attribute viewBox='0 0 width-ratio height-ratio'

Examples:

html,
body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen",
        "Ubuntu", "Cantarell", "Fira Sans",
        "Droid Sans", "Helvetica Neue", sans-serif;
    margin: 0;
    padding: 0;
}
body {
    margin: 1rem;
}

.row {
  padding: 8px 0px;
}

.block {
  display: inline-block;
  vertical-align: top;
  position: relative;
  margin-left: 8px;
  margin-right: 8px;
}

.block-content {
  position: absolute; 
  top: 0; 
  left: 0; 
  right: 0; 
  bottom: 0; 
  display: flex; 
  justify-content: center; 
  align-items: center;
}

.ratio--width-to-height {
  height: 100%; 
  width: auto;
}

.ratio--height-to-width {
  height: auto; 
  width: 100%;
}

<h1>
  Block aspect ratio with svg image
</h1>

<h2>
  width to height
</h2>

<div class="row">   
  <div class="block" style="background: lime; height: 120px;">
    <img class="ratio--width-to-height" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1 1'&gt;&lt;/svg&gt;">
    <div class="block-content">1 : 1</div>
  </div>

  <div class="block" style="background: cyan; height: 120px;">
    <img class="ratio--width-to-height" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 2 1'&gt;&lt;/svg&gt;">
    <div class="block-content">2 : 1</div>
  </div>
  
  <div class="block" style="background: orange; height: 120px;">
    <img class="ratio--width-to-height" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1 1.25'&gt;&lt;/svg&gt;">
    <div class="block-content">1 : 1.25</div>
  </div>
</div>

<h2>
  height to width
</h2>

<div class="row">   
  <div class="block" style="background: lime; width: 120px;">
    <img class="ratio--height-to-width" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1 1'&gt;&lt;/svg&gt;">
    <div class="block-content">1 : 1</div>
  </div>

  <div class="block" style="background: cyan; width: 120px;">
    <img class="ratio--height-to-width" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 2 1'&gt;&lt;/svg&gt;">
    <div class="block-content">2 : 1</div>
  </div>
  
  <div class="block" style="background: orange; width: 120px;">
    <img class="ratio--height-to-width" 
    src="data:image/svg+xml;utf8,&lt;svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1 1.25'&gt;&lt;/svg&gt;">
    <div class="block-content">1 : 1.25</div>
  </div>
</div>

Same example on codepen https://codepen.io/forceuser/pen/MMWBBx

回答3:

max-width / max-height worked for me:

An image of definite size is set in a div (.box).

.parent {
       position: absolute;
}

.box {
    width: 100%;
    height: 100%;
}

.box img {
   max-width: 100%;
   max-height: 100%;
}

来源：https://stackoverflow.com/questions/21799852/css-width-same-as-height

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