<!DOCTYPE html>
<!--
 | The value "break-word" of property "overflow-wrap" does not allow an
 | unbreakable word to be broken at an arbitrary point if there are earlier
 | acceptable break points in the line. It instead wraps to the next line.
 |   https://www.w3.org/TR/css3-text/#overflow-wrap-property
 -->
<html>
<head>
  <style>
    body {
      margin: 0px;
      font-family: Roboto;
      font-size: 20px;
    }
    span {
      overflow-wrap: break-word;
    }
    .containing-block {
      background-color: #03a9f4;
      width: 200px;
    }
  </style>
</head>
<body>
  <div class="containing-block">
    <span>abcdefghijklm nopqrstuvwxyz</span>
  </div>
</body>
</html>