Important Instructions For These Options:

1. 100% - Your values added up cannot go over 100% or your sidebar will not show.

2. PADDING - Is always multiplied by 2 because it adds left and right padding. So a padding value of 5, actually equals 10. And you should only use padding if you are using a background color that is different than your main background color.

3. UNSEEN SPACE - You need to factor in the space between the Content Width & Sidebar Width. This space does not have a field.

EXAMPLE 1: Content Width = 65 + Sidebar Width = 30 + Padding = 0 * this example adds up to 95% which leaves you 5% in between the content and sidebar sections. This is good to use if your sidebar background is the same color as your main background

EXAMPLE 2: Content Width = 60 + Sidebar Width = 30 + Padding = 2.5 * this example adds up to 95% which leaves you 5% in between the content and sidebar sections. This is good to use if your sidebar background is a different color than your main background

Reference

Reference