[style] Center search cursor and hide placeholder
The search bar doesn't feel right if the placeholder is centered,
while the text cursor is left-aligned. The cursor should appear
instead of the placeholder (at the same position).
Added styles to center the text cursor and hide the placeholder
when selecting the input field.
Tested in:
- Firefox 54 & 55
- Chromium 60 (compatible with Chrome 60)
- Microsoft Edge (partially working!)
--- Microsoft Edge ---
Due to a bug in the Microsoft Edge browser, the text cursor is not
centered as long as the placeholder is defined (which it is always)
More information:
https://stackoverflow.com/a/33224868
Official bug report:
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/4468563/
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