Bring the cursor to the top bar, double click on it and the card will go on full-screen.
Try to hover the mouse at the above edge of the full-screen window. After hover, you will see that header will come down. Double-clicking on it will un-full screen the card 🙂
When the card is at full-screen the header automatically disappears. However, you can find a pin on the above right corner using which you can avoid header hiding on full-screen.