I avoid fiddling with borders unless it's the very last thing and I have nothing better to do
It never comes out quite right without a lot of fiddling. I think this is because, first, a spreadsheet is not a table. A table is what we want, but that's not the way Calc works. And second, a spreadsheet is not a platform for creating applications or forms. Again, that's what we want, but it's not what a spreadsheet is designed to do. Finally, Calc has not had the benefit of years of intensive tweaking (like Excel) to make it do those things we want but that spreadsheets don't do well.
All that aside, you may find things go somewhat easier if you change the color of the grid lines under Tools > Options > OO.org > Appearance > Spreadsheet > Gridlines.
I generally set them to some (very) light color and leave it at that, but you can set them to white and then add borders where you want them.
Note: that setting is for the application; it isn't stored in the sheet and it won't have any effect on the appearance of the sheet when someone else opens it. If you're concerned about the appearance when someone else opens the document, you're building an application and that's not what Calc is. If you need absolute control over the appearance, send them a pdf
I've never had much luck trying to use cell styles to apply a border, because I want the border to be independent of the other formatting in a cell but the styles combine everything together. You have to have separate styles for every different combination of border and the other formatting. It works better to just add the borders directly, after all the other formatting is finished.