When you invest in instruments traded on a foreign stock exchange, always make sure to check the currency of the instrument. If it differs from your account's base currency, the exchange rate of the relevant currency pair which is applied to your live result needs to be taken into account.
For example, if your account currency is GBP and you have invested in USD stocks, the exchange rate between the GBP and US dollar can cause your trade’s value to vary.
You may find the already calculated impact of the exchange rate in the "Your investment" section under FX impact.
NOTE: As the opening hours of the FOREX market and the stock exchange markets are different, any currency pair may fluctuate and therefore even when the market is closed, your position's result may fluctuate, too, based on the exchange rate.