I checked and your .work and .end are showing up for me on mobile.
The reason your media changes aren’t showing is usually because your selectors aren’t selecting the right (or any) elements. Also, in the case of
float: center, there isn’t actually a center option for the float setting, so you’ll have to find another way to create the appropriate margin on both sides (hint, hint!).
Other than that one, make sure you’re selecting the correct elements. In your page,
.body doesn’t select anything, because it’s looking for an element with the body class. In another case, changing the color of text in your
nav elements works, but you only have links within your nav element - to change the color of those links you should target the links directly, not the parent container. Where you are centering text, you need to ask yourself if you want the text to be centered, or do you want the link itself to be centered?
To address this last one, I strongly recommend to search for an explanation of the “box model” as I think it’ll really help you position things and position the correct things. Once you have a good grasp of the box model, consider looking at working on some flexbox, for example I really enjoyed the free game flexbox zombies. But you need to understand the box model first.
Edit to add: A pretty handy reference to what is (and is not!) a valid argument for various settings (such as float) is http://devdocs.io/, it lists all of the options for different settings and what arguments they can take, as well as example usage.