Okay, this is what I just tested on my journal, which seems to work (and you should be able to see it there still):
span.cuttag + b {font-size:0px}
span.cuttag + b a {font-size:1rem}
1rem may be the wrong height for you (a rem is equal to the font size of the document root element, which may be something whacky) - you can't use em or percentages, because those are relative to the parent element above it (and anything times 0 is... still 0), but you should be able to use partial rems or points or px.
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span.cuttag + b {font-size:0px} span.cuttag + b a {font-size:1rem}1rem may be the wrong height for you (a rem is equal to the font size of the document root element, which may be something whacky) - you can't use em or percentages, because those are relative to the parent element above it (and anything times 0 is... still 0), but you should be able to use partial rems or points or px.