There's already a gradient on your profile background, unless that's not what you're referring to, I could also give you the selectors for the other stuff if you'd like, you just have to specify what elements

For the buttons you could add the gradient to the primary colour box, but that would also affect others using the primary colour like the navigation bar, so if you're not looking to do that then you could use the selectors .button and button, one which affects links with the button class and the other which affects those using the button html element
While the above does add gradients to all the buttons it also adds it to the ones in the navigation bar, so if you want to remove that as well then, you'd use the .button:not(nav .button) and button:not(nav button) selectors