Ok for the 50%. It looks ok !

For the margin around the button I thought I removed them. I'll look into it. Maybe bootstrap add some by default we need to reduce.
Does it cause any issue in layout having the red margins above ?

I don't mind the padding as is, as long as it is symmetrical. The way the margins are added currently (on top of the padding), there is more space on the right than the top.

Quarto is unbalanced with more space on top than the right, which also bothers me!

I would do .5rem all around.

I don't think the margins are needed here anymore now (red background color added here to help visualize):

I know understand you are talking about the margin of the pre, is that it ?
I am seeing that in the screenshot looking at what rule you deactivated.

The current margin on the pre create a gap between the button and the right side of the pre block when you add the red background.
This margin on the pre is there by designed I believe to have the background of code block spread completely from left to right. (Which lead also to change in block for #1084

Currently, <button> have no margins and padding is the rule sets by bootstrap.

I don't mind the padding as is, as long as it is symmetrical.

What we could do is move the copy button to the right to be coherent with the pre background.

If we want to reduce the red background padding, it would mean changing bootstrap default.

Possibly this would need to be done at the bootstrap variable level maybe ?

• rule for .btn using button_size() mixin on $padding-base-vertical and $padding-base-horizontal
  https://github.com/rstudio/bslib/blob/0650d9d8dec17cb81fafc351efe2ec11da1ac16e/inst/lib/bs3/assets/stylesheets/bootstrap/_buttons.scss#L20

• button_size() sets the padding with the above values
  https://github.com/rstudio/bslib/blob/0650d9d8dec17cb81fafc351efe2ec11da1ac16e/inst/lib/bs4/scss/mixins/_buttons.scss#L105

I am tweaking a lot of things at CSS level currently, but we should leverage bslib better maybe. the bs4_book.css could have been a bs4_book.scss at some point. 😄

Updated example: https://cderv.github.io/bs4booktesting/with-scroll/final-words.html