How can I put the command, Format > Cells > Borders on a toolbar?

I want to click a button, and have the Format > Cells dialog box open up, with the Borders tab selected. The default cell-border button, on the formatting toolbar, applies default lines; you have to go back and open the Format > Cells dialog box, anyway, to set the line width.
I tried to record a macro, but, when the dialog box opened, and I picked the Borders tab, I could not stop recording the macro at that point. I tried, and the dialog box disappeared.

Hello CaseSensitive, to add such a button to an existing Toolbar, you could do this:

1) select the menu Tools:Customize,
2) select the tab "Toolbars",
3) in the dropdown menu "LibreOffice Calc Toolbars" select the toolbar in which you want to add the new button (e.g. the toolbar "Formatting" ),
4) click on the "Add..." button on the right,
5) in the listbox "Category" select the item called "Format",
6) in the listbox "Commands" select the item called "Format Cells",
7) then click on the "Add" button

Next you can give your new button an icon by clicking on the “Modify…” button and choose “Change Icon…”
Clicking on your newly added button should open up the Format Cells Dialog;
if you select the tab “Borders” and then close the dialog, it should open next time with the tab “Borders” selected.

Thanks. Specific, clear steps. I appreciate your taking the time to spell it out.

you’re welcome :D, glad to read it helped