Remove plain style, to specific.

assets/sass/components/button/_button.scss

@@ -10,9 +10,7 @@
 
 .button,
 %button,
-button,
 [type='button'],
-[type='reset'],
 [type='submit'] {
   @extend %button--disabled;
   // Some styles don't apply to <a> links since they are inline elements by default.
@@ -69,26 +67,6 @@ button,
     color: var(--color-button);
     background: var(--color-button-text);
   }
-
-
-  &--plain {
-    appearance: none;
-    padding: 0;
-    margin: .5rem .75rem;
-    color: currentcolor;
-    background: unset;
-    border: unset;
-    text-shadow: unset;
-
-    &:hover,
-    &:focus-visible,
-    &:active {
-      color: currentcolor;
-      background: unset;
-      text-shadow: unset;
-      scale: 1.15;
-    }
-  }
 }
 
 // The disabled variation should always go last, so that it overrides any