this is a grid-row element with 4/5 and a 1/5th column. these cells are set by quick css to the enfold general options width  – on my case it is 75% / 25%

if you want to have 3 cells – the only thing to have is on the right side the same width in % as your aside width will have than.

so you might have 2/5 – 2/5 – 1/5