Edit in JSFiddle

CSS
HTML
Result

p.small {
  line-height: 0.7;
}

p.big {
  line-height: 1.8;
}

p.size {
  line-height: 40px;
}

<!DOCTYPE html>
<html lang="ko">
  <head></head>
  <body>
    <p>
      This is a paragraph with a standard line-height.<br> 
      The default line height in most browsers is about 110% to 120%.
    </p>
    <p class="small">
      This is a paragraph with a smaller line-height.<br> 
      This is a paragraph with a smaller line-height.
    </p>
    <p class="big">
      This is a paragraph with a bigger line-height.<br> 
      This is a paragraph with a bigger line-height.
    </p>
    <p class="size">
      This is a paragraph. line-height: 40px<br> 
      This is a paragraph. line-height: 40px
    </p>
  </body>
</html>