WordPress/wp-includes/blocks/shortcode/editor.css

[data-type="core/shortcode"] .block-editor-plain-text{
  max-height:250px;
}
[data-type="core/shortcode"].components-placeholder{
  min-height:0;
}

.blocks-shortcode__textarea{
  border:1px solid #949494;
  border-radius:2px;
  box-shadow:0 0 0 transparent;
  font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen-Sans,Ubuntu,Cantarell,Helvetica Neue,sans-serif;
  font-size:16px;
  line-height:normal;
  padding:6px 8px;
  transition:box-shadow .1s linear;
}
@media (prefers-reduced-motion:reduce){
  .blocks-shortcode__textarea{
    transition-delay:0s;
    transition-duration:0s;
  }
}
@media (min-width:600px){
  .blocks-shortcode__textarea{
    font-size:13px;
    line-height:normal;
  }
}
.blocks-shortcode__textarea:focus{
  border-color:var(--wp-admin-theme-color);
  box-shadow:0 0 0 1px var(--wp-admin-theme-color);
  outline:2px solid transparent;
}
.blocks-shortcode__textarea::-webkit-input-placeholder{
  color:rgba(30,30,30,.62);
}
.blocks-shortcode__textarea::-moz-placeholder{
  color:rgba(30,30,30,.62);
  opacity:1;
}
.blocks-shortcode__textarea:-ms-input-placeholder{
  color:rgba(30,30,30,.62);
}