Unfortunately simply using `appearance: textfield;`, or even `-webkit-appearance: textfield;`, doesn't actually hide the "spinner" in number-input elements in e.g. Google Chrome.
Hence we need to use a work-around with the `-webkit-inner-spin-button` rule, however in our CSS code we also have `-webkit-outer-spin-button` currently. According to both [the MDN compatibility data](https://developer.mozilla.org/en-US/docs/Web/CSS/::-webkit-outer-spin-button#browser_compatibility) and also manual testing in Google Chrome Beta 99, the `-webkit-outer-spin-button` rule is no longer necessary and we can thus clean-up the CSS a tiny bit.
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