Use different colors for buttons.

**Is your feature request related to a problem? Please describe.**
All buttons look the same. This makes the usage of the application sluggish because the user has to read what the buttons do.

**Describe the solution you'd like**
Making the delete button red will show more quickly that it will remove something. Making the add button green will show that it will add something. This could also be done for cancel, confirm, discard etc...