Input: support 'transparent' theme

app/soapbox/components/ui/input/input.tsx

@@ -85,9 +85,10 @@ const Input = React.forwardRef<HTMLInputElement, IInput>(
           ref={ref}
           className={classNames({
             'text-gray-900 dark:text-gray-100 placeholder:text-gray-600 dark:placeholder:text-gray-600 block w-full sm:text-sm dark:ring-1 dark:ring-gray-800 focus:ring-primary-500 focus:border-primary-500 dark:focus:ring-primary-500 dark:focus:border-primary-500':
-              true,
-            'rounded-md bg-white dark:bg-gray-900 border-gray-400 dark:border-gray-800': theme !== 'search',
+              ['normal', 'search'].includes(theme),
+            'rounded-md bg-white dark:bg-gray-900 border-gray-400 dark:border-gray-800': theme === 'normal',
             'rounded-full bg-gray-200 border-gray-200 dark:bg-gray-800 dark:border-gray-800 focus:bg-white': theme === 'search',
+            'bg-transparent border-none': theme === 'transparent',
             'pr-7': isPassword || append,
             'text-red-600 border-red-600': hasError,
             'pl-8': typeof icon !== 'undefined',