line-height

line-height: normal;

line-height: 2.5;

line-height: 3em;

line-height: 150%;

line-height: 32px;

<section id="default-example">
  <div class="transition-all" id="example-element">
    Far out in the uncharted backwaters of the unfashionable end of the western
    spiral arm of the Galaxy lies a small unregarded yellow sun.
  </div>
</section>

#example-element {
  font-family: Georgia, sans-serif;
  max-width: 200px;
}

/* Keyword value */
line-height: normal;

/* Unitless values: use this number multiplied
by the element's font size */
line-height: 3.5;

/* <length> values */
line-height: 3em;

/* <percentage> values */
line-height: 34%;

/* Global values */
line-height: inherit;
line-height: initial;
line-height: unset;

/* 理论上，以下所有规则拥有相同的行高 */

div {
  line-height: 1.2;
  font-size: 10pt;
} /* 无单位数值 number/unitless */
div {
  line-height: 1.2em;
  font-size: 10pt;
} /* 长度 length */
div {
  line-height: 120%;
  font-size: 10pt;
} /* 百分比 percentage */
div {
  font:
    10pt/1.2 Georgia,
    "Bitstream Charter",
    serif;
} /* font 简写属性 font shorthand */

.green {
  line-height: 1.1;
  border: solid limegreen;
}

.red {
  line-height: 1.1em;
  border: solid red;
}

h1 {
  font-size: 30px;
}

.box {
  width: 18em;
  display: inline-block;
  vertical-align: top;
  font-size: 15px;
}

<div class="box green">
  <h1>Avoid unexpected results by using unitless line-height.</h1>
  length and percentage line-heights have poor inheritance behavior ...
</div>

<div class="box red">
  <h1>Avoid unexpected results by using unitless line-height.</h1>
  length and percentage line-heights have poor inheritance behavior ...
</div>

<!-- The first <h1> line-height is calculated from its own font-size   (30px × 1.1) = 33px  -->
<!-- The second <h1> line-height results from the red div's font-size  (15px × 1.1) = 16.5px,  probably not what you want -->