<input class="secret-code" type="text" accesskey="c" tabindex="-1"
  value="" placeholder="Secret Code" pattern="wow!">

<div style="--wow: var(--secret_code) green; color: var(--wow, black);">
  Focus this window<br>
  (windows) Type [Alt] + c<br>
  (OSX) Type [Control] + [Alt] + c<br>
  This focuses the secret code box.<br>
  Now type the phrase "wow!" without quotes<br>
<span style="--wow: var(--secret_code) block; display: var(--wow, none);">
  <a href="https://www.w3schools.com/tags/att_global_accesskey.asp">
    Learn more about accesskey
.secret-code:not(:placeholder-shown):valid ~ * { --secret_code: ; }
.secret-code { position: absolute; opacity: 0; pointer-events: none; }

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