title: timezone conversion using date-fns
body: <p>I’m trying to work with date-fns-tz in my react-based webpage and couldn’t make the following use-case to work.</p>
  <p>I have a date input in a form that should be submitted to the backend that stores the data in local timezone.</p>
  <p>A user in <strong>GMT+2</strong> timezone selects <strong>14:00 on 1/Feb/2021</strong> in the UI, which correlates to <strong>1612180800</strong> timestamp (as the UI was opened in GMT+2), but it should eventually get sent to the backend as 14:00 in <strong>GMT-8</strong>, which is actually <strong>1612216800</strong> timestamp.</p>
  <p>What’s the right way to get this conversion (from 1612180800  --&gt; 1612216800 ) to work?</p>
  <p>I tried to work with various date-fns functions, but hadn’t found the right one.</p>