The slider has the problem that it cannot dynamically size with the container width, and the amount of slider elements has to be known at compiletime (width: n * 100%).
File upload has the nastiness that you can not really independently style the inputbox with the filename and the button. Chrome has input[type="file"]::-webkit-file-upload-button, but I am not aware of a Firefox/IE solution. Also, you cannot combine the input[type="file"]::-webkit-file-upload-button with a general button selector in the same CSS rule, because Firefox doesn't know the ::-webkit-file-upload-button and discards the whole rule as invalid - you have to double declarate your button styles if you want uniform button look in Chrome. And, even on Chrome, you cannot visually separate the inputbox from the button (e.g. I have a 2-col layout, 320px/col and 16px margin, and I only can mess around with width, padding and margin instead of a clean separation).
To the people who whine about SASS: you can ALWAYS write the resulting CSS by hand, it just takes a boatload of manual typing.