Chrome Version: 70.0.3534.4 (Official Build) dev (64-bit)
OS: Linux

What steps will reproduce the problem?
(1)load the attached testcase
(2)
(3)

What is the expected result?
Three identical fieldset renderings.  The bottom two should render as the top one.

What happens instead?
The bottom two fieldsets have no gap under the border.  It appears they are affected by the height:0 and max-height:10px values which should only affect the content area.  If I understand the fieldset spec correctly, the gap above/below the fieldset's rendered border should inflate the fieldset's border area and thus shouldn't be affected by height/max-height.

https://whatpr.org/html/3934/rendering.html#the-fieldset-and-legend-elements:'block-size'

The rendering in Chrome doesn't make sense to me because the height of the blue area is less than 200px which implies the top and borders overlap and hence that the content-box block-size is less than zero.  The fieldset spec specifies explicitly that "If the content block-size would be negative, let the content block-size be zero instead".

Fwiw, I think Firefox handles this per spec.  The way we implement this is that we apply the [min-|max-]block-size properties to the inner anonymous box instead and essentially flow the outer fieldset box as if it's auto-sized.
 

Deleted: fieldset-borders.html 521 bytes

fieldset-borders.html 521 bytes View Download