Font style declarations + CSS cleanup

- Font family in base is defined for `<body>` and then again for `<h*>`, `<p>` etc. which is unnecessary and makes overriding the default font very tedious in user CSS. Declaring it once on the body and then removing from everything else
- Font styles are declared in short-hand which again make the font declaration tedious to override. To tweak the line height one needs to define all three (family, size and line height). Splitting the font style declaration into `font-family`, `font-size` and `line-height`
- In the form.css, I've kept the `font-family` throughout as Mike mentioned that they are required for overriding the browser styles
- Removed a couple duplicate property declarations