-webkit-text-stroke-width

/* Keyword values */
-webkit-text-stroke-width: thin;
-webkit-text-stroke-width: medium;
-webkit-text-stroke-width: thick;

/* <length> values */
-webkit-text-stroke-width: 2px;
-webkit-text-stroke-width: 0.1em;
-webkit-text-stroke-width: 1mm;
-webkit-text-stroke-width: 5pt;

/* Global values */
-webkit-text-stroke-width: inherit;
-webkit-text-stroke-width: initial;
-webkit-text-stroke-width: revert;
-webkit-text-stroke-width: revert-layer;
-webkit-text-stroke-width: unset;

p {
  margin: 0;
  font-size: 4em;
  -webkit-text-stroke-color: red;
}

#thin {
  -webkit-text-stroke-width: thin;
}

#medium {
  -webkit-text-stroke-width: 3px;
}

#thick {
  -webkit-text-stroke-width: 1.5mm;
}

<p id="thin">Thin stroke</p>
<p id="medium">Medium stroke</p>
<p id="thick">Thick stroke</p>