The accesskey global attribute provides a hint for generating a keyboard shortcut for the current element. The attribute value must consist of a single printable character (which includes accented and other characters that can be generated by the keyboard).
<p>If you need to relax, press the
<strong><u>S</u></strong>tress reliever!</p>
<button accesskey="s">Stress reliever</button>
Source: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/accesskey