my inventory and the game menu are a lot smaller

 

What I expected to happen was...:
nothing because i acidentally clicked the fullscreen button and then my inventory and the game menu became smaller

What actually happened was...:
the game menu became smaller and the game menu to 

Steps to Reproduce:
1. go to the game menu 
2. click on options
3. click on fullscreen

4. and then i did something that did this