Pascal says:
“I can’t remove the parent styling such as underline, colour, and strikethrough of the ins and del tags.”
You should be able to alter any CSS property, but in this case it’s likely being overridden by something you’ve set previously.
If you’ve got the web developer toolbar, press ctrl+shift+y, or whatever the macquivalent is and click the element in question; it’ll bring up all the styles applying to it. Using more accurate selectors you should be able to overcome this.
As a last resort if you can’t work it out, you can force a style using !important. For instance ins{border-bottom:none !important;} The side-effect is that all browsers rendering that instruction think it’s important, and there’s no telling what troubles that might cause in the long run.
I do hope this helps.