The problem with your CSS is that it is being overridden by this:
div.art-content-layout div.art-layout-cell,
div.art-content-layout div.art-layout-cell div.art-content-layout div.art-layout-cell {
display: table-cell;
}
You can make your selector more specific like this:
.art-content-layout .artsidebar1.leftside {
display: none;
}
Or you can just put !important after the one you already have. By the way, "width: 0px;" is meaningless to an element that is already display:none - display:none makes the element act like it isn't in the DOM at all, meaning it could have any width and height and would still not show up on the screen.
As for Mobile Kit Pro, it is very adaptable. You can do virtually anything with it that you could with any other skin, but it comes built with a jQuery UI built-in-theme. If you're looking for ease of use/customization then the jQuery UI themeroller is a good bet, but if you need something more specifically designed I suggest you just use the layout.master and theme.skin and relevant js files from the mobile kit skin, and then put in your own custom CSS files in to make it look how you like.
Also, if you have custom markup in your desktop skins layout.master you could duplicate it, edit it as needed to fit on mobile, and then just copy the mobile kit pro menu portal from the layout.master in that skin. This menu is a great solution for phones, so I suggest using it - you can style it to look pretty much however you want it. I've built a lot of different skins using this menu and it's pretty easy if you know CSS fairly well.
Good luck!
-Isaac