Add warning to Customizer about Firefox bug

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Add docs for #15340

border-radius CSS property doesn't affect <select>s in some browsers.
Hence, @input-border-radius doesn't affect <select class="form-control"> in some browsers.
Closes #15340.

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Add woff2 font in readme.md

Correction in the documentation, add the brand-primary true color in comment and woff2 glyphicons

Make skip link look less "bare bones"

Additional markup for the skip link (to ensure it has the same effective
width as the main content, and to provide an outline around just the
link text) plus some basic styles...make it look a bit more in keeping
with the overall look and feel of the docs.

bump grunt-saucelabs to ~8.4.0

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bump remarkable to ~1.5.0

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use npm-shrinkwrap ^200.0.0

Revert "fix typo in carousel doc"

fix typo in carousel doc

Add @patrickhlauke to Core Team list on the About page

Fix/merge advice on low percentage progress bars

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- actually add the ``min-width`` extra style (and use ``em`` rather than
``px``) to the 0% and 2% example
- remove the unnecessarily redundant sentence in the "With labels"
section
- remove the unnecessary heading/section specifically for low percentage
case, make it flow naturally as part of the "With labels" section