Autocomplete not usable in high contrast mode on Windows

[crisbeto]

The autocomplete has a few issues which prevent high-contrast users from being able to use it:

1. The input bottom border isn't visible, which makes it impossible to figure out that component is an input.
2. The Windows high contrast settings render out all of the borders. This causes a weird thick border above the input which is only used for spacing and is usually transparent.
3. There's no visible indication with regards to what option is highlighted.
4. There is no outline around the autocomplete panel.

A couple of screenshots for reference:

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