The same lining-up rule, plus borrowing across the decimal point.
Start with · Subtract
Enable JavaScript in your browser to calculate.
Column addition with the carried digits written where they actually go.
Regrouping shown the way it is written on paper — crossed out, with the new number above.
When the neighbour is a zero it has nothing to lend, so you keep going left. The hardest one in the unit.
Line up the points, fill the gaps with zeros, then add like normal.