::first-line

p::first-line {
  font-size: 1.2rem;
  font-weight: bold;
  text-decoration: underline;
}

<p>
  In warm ocean waters around the world, you may see a strange sight: A fish
  leaping from the water and soaring dozens of meters before returning to the
  ocean's depths. Early Mediterranean sailors thought these flying fish returned
  to the shore at night to sleep, and therefore called this family of marine
  fish Exocoetidae.
</p>

::first-line {
  /* ... */
}

<p>
  Styles will only be applied to the first line of this paragraph. After that,
  all text will be styled like normal. See what I mean?
</p>

<span>
  The first line of this text will not receive special styling because it is not
  a block-level element.
</span>

* {
  font-size: 20px;
  font-family: sans-serif;
}

::first-line {
  color: blue;
  font-weight: bold;

  /* WARNING: DO NOT USE THESE */
  /* Many properties are invalid in ::first-line pseudo-elements */
  margin-left: 20px;
  text-indent: 20px;
}

<svg viewBox="0 0 320 150">
  <text y="20">Here is an English paragraph
that is broken into multiple lines
in the source code so that it can
be more easily read and edited
in a text editor.
  </text>
</svg>

text {
  font-size: 20px;
  font-family: sans-serif;
}

text {
  white-space: break-spaces;
}

text::first-line {
  fill: blue;
  font-weight: bold;
}