Remove Flash of field color on tap when filling out form on mobile

Highlighted
Explorer
96 0 4

Using debut. Kind of hard to explain, and I can't get a photo of it because it is so quick, but on mobile, when I tap a form label or field, there's a flash of grey. Like a block of grey background that appears and disappears. My form field borders are set to none. How can I remove this problem? My theme.scss.liquid form code is set to the original code supplied by Shopify, except I set the border to none:

input,
textarea,
select {
  border: none;
  background-color: $color-text-field;
  color: $color-text-field-text;
  max-width: 100%;
  line-height: 1.2;
  border-radius: $border-radius;
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Highlighted
Explorer
96 0 4

*This can also be described as a "highlight"

My code below is set to transparent but my form fields are still getting a flash of grey highlight on tap:

-webkit-tap-highlight-color: transparent;
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