Is there a way to make numbers in an ordered list bold?

A new ::marker pseudo-element selector has been added to CSS Pseudo-Elements Level 4, which makes styling list item numbers in bold as simple as

ol > li::marker {
  font-weight: bold;
}

It is currently supported by Firefox 68+, Chrome/Edge 86+, and Safari 11.1+.

Counter-increment

CSS

ol {
  margin: 0 0 1.5em;
  padding: 0;
  counter-reset: item;
}

ol > li {
  margin: 0;
  padding: 0 0 0 2em;
  text-indent: -2em;
  list-style-type: none;
  counter-increment: item;
}

ol > li:before {
  display: inline-block;
  width: 1em;
  padding-right: 0.5em;
  font-weight: bold;
  text-align: right;
  content: counter(item) ".";
}

DEMO