You can change the Theme here:
But you won't get a 'dark' theme. For this you need a more recent Eclipse version. Not sure what device/microcontroller you are using. I suggest you use the MCUXpresso IDE which supports dark and darkest themes (see Installing Darkest Theme with MCUXpresso IDE 10.2 | MCU on Eclipse which describes it for 10.2). The current MCUXpresso IDE is 10.3.0 and comes with the Dark Theme pre-installed:
I hope this helps,
Erich