Changing size of sidebar

Hello everyone please help me
I want to change size of sidebar. I want to reduce its size and increase the size of main content.

Hello there,

I hope you are doing well today.

You can use the following CSS code to adjust the size of the sidebars by going to Appearance > Customize > Additional CSS and pasting it there.

/*Sidebar width*/
.col-md-4 {
    width: 30%;

/*Main section*/
.col-md-8 {
    width: 70%;

Best Regards,