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HTML

              
                <h1>
    line-height lock<br>
    1.4 ➡ 1.8
</h1>

<p class="standard"><em>The line-height of the paragraphs goes from 140% to 180% between two breakpoints (20em and 60em, i.e. 320px and 960px with default settings). The smaller gray numbers are the actual line-height as a ratio, computed with JS.</em></p>

<p class="bigger">Bigger text — Lorem ipsum dolor sit amet, consectetur adipisicing elit. Aut consequuntur distinctio enim iure nesciunt officia quia saepe veritatis? Ab aliquid dolor iste mollitia provident soluta voluptas? Distinctio dolore tempore tenetur!</p>

<p class="standard">Ab aliquam at blanditiis cum delectus eaque ex fuga, fugit hic, illo impedit laborum natus nesciunt nisi nostrum placeat ratione rerum sequi similique sit? A corporis debitis delectus deserunt ea eos harum libero maiores necessitatibus nemo nobis odio omnis, placeat quasi, rerum sunt voluptatem! Dignissimos enim, facilis illo itaque nemo tempore. Adipisci, eos, illum.</p>
              
            
!

CSS

              
                /* CSS locks */
p {
  line-height: 1.4;
}
.bigger {
  font-size: 166%;
}
@media (min-width: 20em) {
  .standard {
    line-height: calc( 140% + .4 * (100vw - 20rem) / (60 - 20) );
  }
  .bigger {
    line-height: calc( 140% + .4 * 1.66 * (100vw - 20rem) / (60 - 20) );
  }
}
@media (min-width: 60em) {
  .standard,
  .bigger {
    line-height: 1.8;
  }
}

/* Show the computed line-height (as a ratio) */
[data-lh]::before {
  content: attr(data-lh);
  display: inline-block;
  vertical-align: 15%;
  padding: 2px 4px 3px;
  border-radius: 3px;
  margin-right: 5px;
  font-size: 14px;
  line-height: 1;
  color: #fff;
  background-color: #777;
}

/* Cosmetic styles */
body {
  font-family: Helvetica Neue, Arial, sans-serif;
  max-width: 720px;
  margin: 60px auto;
  padding: 0 20px;
  /* Just for fun, let’s size the main column relative to vw too */
  width: calc( 100px + 50vw );
}
h1 {
  margin: 1.25em 0;
  font-size: 300%;
  line-height: 1.2;
}
              
            
!

JS

              
                var paragraphs = document.querySelectorAll('p');
function updateInfo() {
    Array.prototype.forEach.call(paragraphs, function (p) {
        var styles = getComputedStyle(p);
        var lh = parseFloat(styles.lineHeight.replace('px', ''));
        var fs = parseFloat(styles.fontSize.replace('px', ''));
        var ratio = Math.round((lh / fs) * 100) / 100;
        p.setAttribute('data-lh', '' + ratio);
    });
}
window.addEventListener('resize', updateInfo);
updateInfo();
              
            
!
999px

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