您可以调整该字母的line-height，它将关闭间隙：

.first-word-uppercase-p::first-letter {
  font-size: 40px;
  color: #e80222;
  font-weight: bold;
  line-height: .75;
}

<p class="first-word-uppercase-p">
  There is no doubt that people find out who they really are when their backs are against the wall. Such was the case for Sara Owen, a single mother who found herself without the ability to make ends meet and provide for her three children. "I wasn't broke,
  but times were tough," says Sara, who even found herself having to hide from her landlord on occasion. But everything changed when Sara decided that she was going to take her destiny into her own hands. "I was thinking about investing in stocks for
  several years, but I could never find the courage to do it. Little did I know that I would turn $200 into $2000 in only a matter of days.
</p>

在main元素上设置一个固定的line-height，第一个字母将继承它。这将适用于所有font-size配置

.first-word-uppercase-p {
  line-height:1.2em;
}

.first-word-uppercase-p::first-letter {
  font-size: 40px;
  color: #e80222;
  font-weight: bold;
}

.first-word-uppercase-p.bigger::first-letter {
  font-size:50px;
}

<p class="first-word-uppercase-p">
  There is no doubt that people find out who they really are when their backs are against the wall. Such was the case for Sara Owen, a single mother who found herself without the ability to make ends meet and provide for her three children. "I wasn't broke,
  but times were tough," says Sara, who even found herself having to hide from her landlord on occasion. But everything changed when Sara decided that she was going to take her destiny into her own hands. "I was thinking about investing in stocks for
  several years, but I could never find the courage to do it. Little did I know that I would turn $200 into $2000 in only a matter of days.
</p>

<p class="first-word-uppercase-p bigger">
  There is no doubt that people find out who they really are when their backs are against the wall. Such was the case for Sara Owen, a single mother who found herself without the ability to make ends meet and provide for her three children. "I wasn't broke,
  but times were tough," says Sara, who even found herself having to hide from her landlord on occasion. But everything changed when Sara decided that she was going to take her destiny into her own hands. "I was thinking about investing in stocks for
  several years, but I could never find the courage to do it. Little did I know that I would turn $200 into $2000 in only a matter of days.
</p>