Fix border colors search input field for Safari

[rianrietveld]

From the accessibility audit, issue #232

SC 1.4.11 Non-text Contrast: In Safari the search form input field's lower and right borders have a very light color (#D5DADD). This has a contrast rate of 1,.7:1 with the main background color (#fcfcfc). If you make this the same color as the upper border (#333435) the contrast ratio is excellent. Seen on all pages, e.g. https://wpaccessibility.org/ (The button uses a different shade of gray (#848789), maybe they should all be the same.)

The work:
Fix the color contrast.