you can set the width of your layout in General options tab.
Instead you can't set the height of elements with a ready option. To do this, you must use CSS style drag and drop builder, from Style tab. You must select your item (by id or class) and add the height property and value to it.
The causes can be so many. Maybe another CSS rule is overriding your, maybe the rule is not properly set.
You can instead turn on "Advanced settings" in component options, write your own CSS code in "Advanced" tab into the layout editor and delete the style rules in drag and drop editor.