The units for 0 values in CSS are redundant. This is a quick no-op change that makes the code more concise and readable as the unitless 0 is distinguished from hard-set values with units.
Read more: https://stackoverflow.com/q/7923042/13079675
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This technically depends on D4339 since both diffs modify `landing/subscription-form.css`, but I can resolve that merge conflict quickly and easily.