i want to cover the black space below the comment with column. And when we expend the comment then column size get auto reduce.
Discussion posts and replies are publicly visible
You can apply the condition on the width of the comment column and keep the other column on AUTO. If the comment is visible (ie. local!showComments=true) then set the width to NARROW otherwise keep it EXTRA_NARROW. You will also have to hide the Comments text as it will not fit in the EXTRA_NARROW so you will have use an icon when the value is false otherwise you can use the name.
More details -> better tips !
Seems like this is a columns layout. Why not just hide the right hand column when your comments are collapsed?