File type inputs are notoriously hard to style, due to different semi-serious style restrictions in the name of security (the argument being that a file input presents access to the user's private file system, and should as such always look unambiguously like what it is — redundant if you ask me since the resulting file upload dialogue is completely out of your control). This allows near enough total style freedom using pure CSS.
Highcharts comes with a configurable `thousandsSep` (short for 'thousands separator') property as part of its localisation (`lang`) options. It has a default value of `,` — which strongly implies that by default, numeric strings will have a comma delimiting thousands. However, even if this option is explicitly set, numeric strings never feature thousands separators. Why is this?