Update file input to remove height and line-height

This particular form control is wildly inaccurate across browsers, so
we're removing the `height` and `line-height`, but adding `display:
block` so it renders similarly to our other inputs.

css.html

@@ -1170,6 +1170,8 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
         <input type="text" id="exampleInputEmail" placeholder="Enter email">
         <label for="exampleInputPassword">Password</label>
         <input type="text" id="exampleInputPassword" placeholder="Password">
+        <label for="exampleInputFile">File input</label>
+        <input type="file" id="exampleInputFile">
         <p class="help-block">Example block-level help text here.</p>
         <div class="checkbox">
           <label>