diff --git a/sphinx/texinputs/sphinx.sty b/sphinx/texinputs/sphinx.sty
index 4915ecba00..b1b2be34a7 100644
--- a/sphinx/texinputs/sphinx.sty
+++ b/sphinx/texinputs/sphinx.sty
@@ -171,7 +171,6 @@
 \sphinxDeclareSphinxColorOption{attentionBorderColor}{{rgb}{0,0,0}}
 \sphinxDeclareSphinxColorOption{dangerBorderColor}{{rgb}{0,0,0}}
 \sphinxDeclareSphinxColorOption{errorBorderColor}{{rgb}{0,0,0}}
-% 5.1.0 section redefines the keys for BackgroundColor CSS-like naming
 \sphinxDeclareSphinxColorOption{warningBgColor}{{rgb}{1,1,1}}
 \sphinxDeclareSphinxColorOption{cautionBgColor}{{rgb}{1,1,1}}
 \sphinxDeclareSphinxColorOption{attentionBgColor}{{rgb}{1,1,1}}
@@ -427,7 +426,164 @@
     \spx@topic@withshadowcolortrue
     \definecolor{sphinxTopicShadowColor}#1%
 }
-%
+% warning, caution, attention, danger, error
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+% MEMO: the diverging naming of first one is conditioned at this time by the fact 
+% that sphinxnotice environment must work both for these admonitions and the
+% note, tip etc... ones
+  \csname spx@opt@#1border\expandafter\endcsname
+  \csname spx@#1@border@top\expandafter\endcsname
+  \csname spx@#1@border@right\expandafter\endcsname
+  \csname spx@#1@border@left\expandafter\endcsname
+  \csname spx@#1@border@bottom\expandafter\endcsname
+  \csname ifspx@#1@border@open\expandafter\endcsname
+  \csname spx@#1@border@opentrue\expandafter\endcsname
+  \csname spx@#1@border@openfalse\endcsname
+  {#1}%
+}%
+\def\spx@tempb #1#2#3#4#5#6#7#8#9{%
+  \define@key{sphinx}{div.#9_border-top-width}{\def#2{##1}}%
+  \define@key{sphinx}{div.#9_border-right-width}{\def#3{##1}}%
+  \define@key{sphinx}{div.#9_border-bottom-width}{\def#4{##1}}%
+  \define@key{sphinx}{div.#9_border-left-width}{\def#5{##1}}%
+  \define@key{sphinx}{div.#9_border-width}{\def#1{##1}\def#2{#1}\let#3#2\let#4#2\let#5#2}%
+  \def#1{1pt}\let#2#1\let#3#2\let#4#2\let#5#2%
+  \newif#6%
+  \define@key{sphinx}{div.#9_box-decoration-break}%
+           {\edef\spx@tempa{##1}%
+            \ifx\spx@tempa\spxstring@clone#8\else#7\fi}%
+  \expandafter\let\csname KV@sphinx@#9border\expandafter\endcsname
+                  \csname KV@sphinx@div.#9_border-width\endcsname
+}
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+  \csname spx@#1@padding\expandafter\endcsname
+  \csname spx@#1@padding@top\expandafter\endcsname
+  \csname spx@#1@padding@right\expandafter\endcsname
+  \csname spx@#1@padding@left\expandafter\endcsname
+  \csname spx@#1@padding@bottom\endcsname
+  {#1}%
+}%
+\def\spx@tempb #1#2#3#4#5#6{%
+  \define@key{sphinx}{div.#6_padding-top}{\def#2{##1}}%
+  \define@key{sphinx}{div.#6_padding-right}{\def#3{##1}}%
+  \define@key{sphinx}{div.#6_padding-bottom}{\def#4{##1}}%
+  \define@key{sphinx}{div.#6_padding-left}{\def#5{##1}}%
+  \define@key{sphinx}{div.#6_padding}{\def#1{##1}\def#2{#1}\let#3#2\let#4#2\let#5#2}%
+  \edef#1{\number\dimexpr.6\baselineskip-1pt\relax sp}% (from legacy coding in sphinxheavybox)
+  \let#2#1\let#3#2\let#4#2\let#5#2%
+  \expandafter\let\csname KV@sphinx@#6padding\expandafter\endcsname
+                  \csname KV@sphinx@div.#6_padding\endcsname
+}
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+  \csname spx@#1@radius@topleft\expandafter\endcsname
+  \csname spx@#1@radius@topright\expandafter\endcsname
+  \csname spx@#1@radius@bottomright\expandafter\endcsname
+  \csname spx@#1@radius@bottomleft\endcsname
+  {#1}%
+}%
+\def\spx@tempb #1#2#3#4#5{%
+  \define@key{sphinx}{div.#5_border-top-left-radius}{\def#1{##1}}%
+  \define@key{sphinx}{div.#5_border-top-right-radius}{\def#2{##1}}%
+  \define@key{sphinx}{div.#5_border-bottom-right-radius}{\def#3{##1}}%
+  \define@key{sphinx}{div.#5_border-bottom-left-radius}{\def#4{##1}}%
+  \define@key{sphinx}{div.#5_border-radius}{\def#1{##1}\let#2#1\let#3#1\let#4#1}%
+  \let#1\z@\let#2#1\let#3#2\let#4#2%
+  \AtBeginDocument{\if1\ifdim#1>\z@0\fi
+    \ifdim#2>\z@0\fi
+    \ifdim#3>\z@0\fi
+    \ifdim#4>\z@0\fi
+    1\else\spx@RequirePackage@PictIIe\fi}%
+}
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+  \csname ifspx@#1@withshadow\expandafter\endcsname
+  \csname ifspx@#1@insetshadow\expandafter\endcsname
+  \csname ifspx@#1@withshadowcolor\expandafter\endcsname
+  \csname ifspx@#1@withbordercolor\expandafter\endcsname
+  \csname ifspx@#1@withbackgroundcolor\endcsname
+}%
+\def\spx@tempb#1#2#3#4#5{\newif#1\newif#2\newif#3\newif#4\newif#5}%
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+  \csname spx@#1@withshadowtrue\expandafter\endcsname
+  \csname spx@#1@withshadowfalse\expandafter\endcsname
+  \csname spx@#1@insetshadowtrue\expandafter\endcsname
+  \csname spx@#1@insetshadowfalse\expandafter\endcsname
+  \csname spx@#1@box@shadow@setter\expandafter\endcsname
+  \csname spx@#1@box@shadow@xoffset\expandafter\endcsname
+  \csname spx@#1@box@shadow@yoffset\endcsname
+  {#1}%
+}%
+\def\spx@tempb#1#2#3#4#5#6#7#8{%
+  \define@key{sphinx}{div.#8_box-shadow}{#5##1 {} {} \@nnil}%
+  \def#5##1 ##2 ##3 ##4\@nnil{%
+  \edef\spx@tempa{##1}%
+  \ifx\spx@tempa\spxstring@none
+        #2%
+  \else #1\edef#6{\number\dimexpr##1\relax sp}%
+          \edef#7{\number\dimexpr##2+\z@\relax sp}%
+    \if\relax\detokenize{##3}\relax#4\else#3\fi
+  \fi     
+  }#5none {} {} \@nnil
+}
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
+\def\spx@tempc#1{%
+  \expandafter\spx@tempb
+  \csname spx@#1@withbordercolortrue\expandafter\endcsname
+  \csname spx@#1@withbackgroundcolortrue\expandafter\endcsname
+  \csname spx@#1@withshadowcolortrue\endcsname
+  {#1}%
+}
+\def\spx@tempb#1#2#3#4{%
+  \definecolor{sphinx#4BorderColor}{rgb}{0,0,0}%
+  \definecolor{sphinx#4BgColor}{rgb}{1,1,1}%
+  \definecolor{sphinx#4ShadowColor}{rgb}{0,0,0}%
+  \define@key{sphinx}{div.#4_border-TeXcolor}{#1\definecolor{sphinx#4BorderColor}##1}%
+  \define@key{sphinx}{div.#4_background-TeXcolor}{#2\definecolor{sphinx#4BgColor}##1}%
+  \define@key{sphinx}{div.#4_box-shadow-TeXcolor}{#3\definecolor{sphinx#4ShadowColor}##1}%
+  \expandafter\let\csname KV@sphinx@#4BorderColor\expandafter\endcsname
+                  \csname KV@sphinx@div.#4_border-TeXcolor\endcsname
+  \expandafter\let\csname KV@sphinx@#4BgColor\expandafter\endcsname
+                  \csname KV@sphinx@div.#4_background-TeXcolor\endcsname
+}
+\spx@tempc{warning}
+\spx@tempc{caution}
+\spx@tempc{attention}
+\spx@tempc{danger}
+\spx@tempc{error}
+
 
 \DeclareDefaultOption{\@unknownoptionerror}
 \ProcessKeyvalOptions*
diff --git a/sphinx/texinputs/sphinxlatexadmonitions.sty b/sphinx/texinputs/sphinxlatexadmonitions.sty
index f78bd6c7f8..3642dfb191 100644
--- a/sphinx/texinputs/sphinxlatexadmonitions.sty
+++ b/sphinx/texinputs/sphinxlatexadmonitions.sty
@@ -66,49 +66,117 @@
 \definecolor{sphinxtipBgColor}{rgb}{1,1,1}
 
 % Others get more distinction
-\def\spx@admonitions@boxes@fcolorbox@init{%
-  \spx@boxes@border@top   \FrameRule
-  \spx@boxes@border@right \FrameRule
-  \spx@boxes@border@bottom\FrameRule
-  \spx@boxes@border@left  \FrameRule
-  \spx@boxes@border       \FrameRule
-  %
-  \spx@boxes@padding@top   \FrameSep
-  \spx@boxes@padding@right \FrameSep
-  \spx@boxes@padding@bottom\FrameSep
-  \spx@boxes@padding@left  \FrameSep
-  %
-%  \spx@boxes@shadow@xoffset\sphinxshadowsize % A REVOIR
-%  \spx@boxes@shadow@yoffset\sphinxshadowsize
+\def\spx@admonitions@boxes@fcolorbox@setup{%
+  \spx@boxes@border@top   \@nameuse{spx@\spx@noticetype @border@top}%
+  \spx@boxes@border@right \@nameuse{spx@\spx@noticetype @border@right}%
+  \spx@boxes@border@bottom\@nameuse{spx@\spx@noticetype @border@bottom}%
+  \spx@boxes@border@left  \@nameuse{spx@\spx@noticetype @border@left}%
+  \spx@boxes@border       \spx@notice@border
+%
+  \spx@boxes@padding@top   \@nameuse{spx@\spx@noticetype @padding@top}%
+  \spx@boxes@padding@right \@nameuse{spx@\spx@noticetype @padding@right}%
+  \spx@boxes@padding@bottom\@nameuse{spx@\spx@noticetype @padding@bottom}%
+  \spx@boxes@padding@left  \@nameuse{spx@\spx@noticetype @padding@left}%
+%
+  \spx@boxes@radius@topleft     \@nameuse{spx@\spx@noticetype @radius@topleft}%
+  \spx@boxes@radius@topright    \@nameuse{spx@\spx@noticetype @radius@topright}%
+  \spx@boxes@radius@bottomright \@nameuse{spx@\spx@noticetype @radius@bottomright}%
+  \spx@boxes@radius@bottomleft  \@nameuse{spx@\spx@noticetype @radius@bottomleft}%
+  \relax
+  \iftrue\@nameuse{ifspx@\spx@noticetype @withshadow}%
+     \spx@boxes@withshadowtrue
+     \spx@boxes@shadow@xoffset \@nameuse{spx@\spx@noticetype @box@shadow@xoffset}%
+     \spx@boxes@shadow@yoffset \@nameuse{spx@\spx@noticetype @box@shadow@yoffset}\relax
+  \else
+     \spx@boxes@withshadowfalse
+  \fi\@nameuse{fi}%
+  \iftrue\@nameuse{ifspx@\spx@noticetype @insetshadow}%
+     \spx@boxes@insetshadowtrue
+  \else
+     \spx@boxes@insetshadowfalse
+  \fi\@nameuse{fi}%
+  \iftrue\@nameuse{ifspx@\spx@noticetype @withshadowcolor}%
+    \spx@boxes@withshadowcolortrue
+  \else
+    \spx@boxes@withshadowcolorfalse
+  \fi\@nameuse{fi}%
   %
-  \spx@boxes@withshadowfalse
-  \spx@boxes@withshadowcolorfalse
-  \spx@boxes@withbackgroundcolortrue
+  \iftrue\@nameuse{ifspx@\spx@noticetype @withbackgroundcolor}%
+    \spx@boxes@withbackgroundcolortrue
+  \else
+    \spx@boxes@withbackgroundcolorfalse
+  \fi\@nameuse{fi}%
   \sphinxcolorlet{spx@boxes@backgroundcolor}{spx@notice@bgcolor}%
-  \spx@boxes@withbordercolortrue
+  %
+  \iftrue\@nameuse{ifspx@\spx@noticetype @withbordercolor}%
+    \spx@boxes@withbordercolortrue
+  \else
+    \spx@boxes@withbordercolorfalse
+  \fi\@nameuse{fi}%
   \sphinxcolorlet{spx@boxes@bordercolor}{spx@notice@bordercolor}%
-}%
+  %
+  \iftrue\@nameuse{ifspx@\spx@noticetype @withshadowcolor}%
+    \spx@boxes@withshadowcolortrue
+  \else
+    \spx@boxes@withshadowcolorfalse
+  \fi\@nameuse{fi}%
+  \sphinxcolorlet{spx@boxes@shadowcolor}{sphinx\spx@noticetype ShadowColor}%
+}
 % Code adapted from framed.sty's "snugshade" environment.
 % Nesting works (inner frames do not allow page breaks).
 \newenvironment{sphinxheavybox}{\par
-   \setlength{\FrameRule}{\spx@notice@border}%
-   \setlength{\FrameSep}{\dimexpr.6\baselineskip-\FrameRule\relax}
+   \spx@admonitions@boxes@fcolorbox@setup
+   % Those are used by sphinxVerbatim if the \ifspx@inframed boolean is true
+   \setlength{\FrameRule}{0.5\dimexpr\spx@boxes@border@top+\spx@boxes@border@bottom\relax}%
+   % Prior to 5.1.0 \FrameSep served to configure the (unique) padding, via
+   % \fboxsep parameter of \fcolorbox; it was determined as 0.6\baselineskip -
+   % borderwidth, increasing borderwidth did not change text location
+   % vertically as borderwidth+padding remained constant.  But this limited
+   % considerably (at most to 4pt or 5pt) the usual borderwidths.
+   % Now \FrameSep is not used, but is needed still by sphinxVerbatim (see
+   % prior comment above).  We give it some reasonable definition.
+   \setlength{\FrameSep}{0.5\dimexpr\spx@boxes@padding@top+\spx@boxes@padding@bottom\relax}%
    \advance\spx@image@maxheight
-   -\dimexpr2\FrameRule
-           +2\FrameSep
+   -\dimexpr\spx@boxes@border@top+\spx@boxes@border@bottom
+           +\spx@boxes@padding@top+\spx@boxes@padding@bottom
            +\baselineskip\relax % will happen again if nested, needed indeed!
+   % MEMO: the next comment is before boxing was extended to allow padding and
+   % multiple border-widths, not to mention shadows...
    % configure framed.sty's parameters to obtain same vertical spacing
    % as for "light" boxes. We need for this to manually insert parskip glue and
    % revert a skip done by framed before the frame.
     \ltx@ifundefined{OuterFrameSep}{}{\OuterFrameSep\z@skip}%
     \vspace{\FrameHeightAdjust}
-   % this will in particular set up colors, formerly passed as first
-   % two arguments of \fcolorbox
-   \let\spx@boxes@fcolorbox@init\spx@admonitions@boxes@fcolorbox@init
    % copied/adapted from framed.sty's snugshade
    % but now using in place of \fcolorbox the Sphinx sophisticated own
    \def\FrameCommand##1{\hskip\@totalleftmargin
-       \spx@boxes@fcolorbox{##1}%
+  \ifspx@boxes@withshadow
+   \ifspx@boxes@insetshadow\else
+    \ifdim\spx@boxes@shadow@xoffset<\z@\hskip\spx@boxes@shadow@xoffset\relax
+    \fi
+   \fi
+  \fi
+        \if1% use rounded boxes only if needed and possible
+          \ifdim\spx@boxes@radius@topleft    >\z@0\fi
+          \ifdim\spx@boxes@radius@topright   >\z@0\fi
+          \ifdim\spx@boxes@radius@bottomright>\z@0\fi
+          \ifdim\spx@boxes@radius@bottomleft >\z@0\fi
+          1\spx@boxes@fcolorbox{##1}%
+        \else
+          \@ifpackageloaded{pict2e}%
+             {\ifspx@boxes@insetshadow
+                \spx@boxes@fcolorbox{##1}%
+              \else
+                \spx@boxes@fcolorbox@rounded{##1}%
+              \fi}%
+             {\spx@boxes@fcolorbox{##1}}%
+        \fi
+  \ifspx@boxes@withshadow
+   \ifspx@boxes@insetshadow\else
+    \ifdim\spx@boxes@shadow@xoffset>\z@\hskip-\spx@boxes@shadow@xoffset\relax
+    \fi
+   \fi
+  \fi
        \hskip-\linewidth \hskip-\@totalleftmargin \hskip\columnwidth}%
    \savenotes
    % use a minipage if we are already inside a framed environment
diff --git a/sphinx/texinputs/sphinxlatexliterals.sty b/sphinx/texinputs/sphinxlatexliterals.sty
index de8c15f1ee..68c9523f42 100644
--- a/sphinx/texinputs/sphinxlatexliterals.sty
+++ b/sphinx/texinputs/sphinxlatexliterals.sty
@@ -219,24 +219,24 @@
 }%
 \def\sphinxVerbatim@FirstFrameCommand{%
     \ifspx@pre@border@open
-      \let\spx@boxes@fcolorbox@init\spx@verb@boxes@fcolorbox@init@openbottom
+      \let\spx@boxes@fcolorbox@setuphook\spx@verb@boxes@fcolorbox@setuphook@openbottom
     \fi
     \spx@verb@FrameCommand\sphinxVerbatim@Before\sphinxVerbatim@Continues
 }%
 \def\sphinxVerbatim@MidFrameCommand{%
     \ifspx@pre@border@open
-      \let\spx@boxes@fcolorbox@init\spx@verb@boxes@fcolorbox@init@openboth
+      \let\spx@boxes@fcolorbox@setuphook\spx@verb@boxes@fcolorbox@setuphook@openboth
     \fi
     \spx@verb@FrameCommand\sphinxVerbatim@Continued\sphinxVerbatim@Continues
 }%
 \def\sphinxVerbatim@LastFrameCommand{%
     \ifspx@pre@border@open
-      \let\spx@boxes@fcolorbox@init\spx@verb@boxes@fcolorbox@init@opentop
+      \let\spx@boxes@fcolorbox@setuphook\spx@verb@boxes@fcolorbox@setuphook@opentop
     \fi
     \spx@verb@FrameCommand\sphinxVerbatim@Continued\sphinxVerbatim@After
 }%
 %
-\def\spx@verb@boxes@fcolorbox@init{% for using \spx@boxes@fcolorbox
+\def\spx@verb@boxes@fcolorbox@setup{%
 %
   \spx@boxes@border@top   \spx@pre@border@top
   \spx@boxes@border@right \spx@pre@border@right
@@ -279,20 +279,17 @@
                             \spx@boxes@withshadowcolorfalse\fi
   \sphinxcolorlet{spx@boxes@shadowcolor}{sphinxVerbatimShadowColor}%
 }%
-\def\spx@verb@boxes@fcolorbox@init@openbottom{%
-    \spx@verb@boxes@fcolorbox@init
+\def\spx@verb@boxes@fcolorbox@setuphook@openbottom{%
     \spx@boxes@border@bottom     \z@
     \spx@boxes@radius@bottomright\z@
     \spx@boxes@radius@bottomleft \z@
 }%
-\def\spx@verb@boxes@fcolorbox@init@opentop{%
-    \spx@verb@boxes@fcolorbox@init
+\def\spx@verb@boxes@fcolorbox@setuphook@opentop{%
     \spx@boxes@border@top     \z@
     \spx@boxes@radius@topright\z@
     \spx@boxes@radius@topleft \z@
 }%
-\def\spx@verb@boxes@fcolorbox@init@openboth{%
-    \spx@verb@boxes@fcolorbox@init
+\def\spx@verb@boxes@fcolorbox@setuphook@openboth{%
     \spx@boxes@border@top     \z@
     \spx@boxes@border@bottom  \z@
     \spx@boxes@radius@topright\z@
@@ -785,8 +782,8 @@
       \let\sphinxVerbatim@Continued\@empty
       \let\sphinxVerbatim@Continues\@empty
   \fi
-  % initialization for sphinxpackageboxes provided \spx@boxes@fcolorbox
-  \def\spx@boxes@fcolorbox@init{\spx@verb@boxes@fcolorbox@init}%
+  % initialization for \spx@boxes@fcolorbox from sphinxpackageboxes.sty
+  \spx@verb@boxes@fcolorbox@setup
   \ifspx@opt@verbatimwrapslines
     % deep hack into fancyvrb's internal processing of input lines
     \let\FV@@PreProcessLine\spx@verb@@PreProcessLine
diff --git a/sphinx/texinputs/sphinxlatexshadowbox.sty b/sphinx/texinputs/sphinxlatexshadowbox.sty
index cfd1e562da..d9a35eb56c 100644
--- a/sphinx/texinputs/sphinxlatexshadowbox.sty
+++ b/sphinx/texinputs/sphinxlatexshadowbox.sty
@@ -18,7 +18,7 @@
 \RequirePackage{framed}
 \RequirePackage{sphinxpackageboxes}
 
-\def\spx@shadowbox@boxes@fcolorbox@init{%
+\def\spx@shadowbox@boxes@fcolorbox@setup{%
 %
   \spx@boxes@border@top   \spx@topic@border@top
   \spx@boxes@border@right \spx@topic@border@right
@@ -115,7 +115,7 @@
 %   adjusting to current text indentation.
 \newenvironment{sphinxShadowBox}
   {%
-   \let\spx@boxes@fcolorbox@init\spx@shadowbox@boxes@fcolorbox@init
+   \spx@shadowbox@boxes@fcolorbox@setup
    \def\FrameCommand {\spx@ShadowFBox }%
    \advance\spx@image@maxheight
    -\dimexpr\spx@topic@border@top+\spx@topic@border@bottom
diff --git a/sphinx/texinputs/sphinxpackageboxes.sty b/sphinx/texinputs/sphinxpackageboxes.sty
index d2e535414f..14d4eb1ed3 100644
--- a/sphinx/texinputs/sphinxpackageboxes.sty
+++ b/sphinx/texinputs/sphinxpackageboxes.sty
@@ -93,17 +93,20 @@
 % colors: background, border and shadow.  Its boundary box takes into account
 % all of shadow, border and padding.
 %
-% The customization of the various parameters are to be done in a macro
-% \spx@boxes@fcolorbox@init which is under responsability of caller.
-\let\spx@boxes@fcolorbox@init\@empty
+% The customization of the various parameters are under responsability of
+% caller.  At some point of code development the parameters were set
+% by expansion of an \spx@boxes@fcolorbox@setup macro inside
+% \spx@boxes@fcolorbox.  Now this is only a hook, because the initialization
+% will be done by caller rather.
+\let\spx@boxes@fcolorbox@setuphook\@empty
 % The same applies to \spx@boxes@fcolorbox@rounded, also with (same name)
-% \spx@boxes@fcolorbox@init left to caller configuration.
+% \spx@boxes@fcolorbox@setup left to caller configuration.
 %
 % The parameters are interpreted as they would as CSS properties.
 % For the shadow inset variant see separate \spx@boxes@fcolorbox@insetshadow
 \long\def\spx@boxes@fcolorbox#1{%
   \hbox\bgroup
-  \spx@boxes@fcolorbox@init
+  \spx@boxes@fcolorbox@setuphook
   \setbox\spx@tempboxa
    \hbox{\kern\dimexpr\spx@boxes@border@left+\spx@boxes@padding@left\relax
          {#1}%
@@ -350,7 +353,7 @@
 
 \long\def\spx@boxes@fcolorbox@rounded #1{%
   \hbox{%
-   \spx@boxes@fcolorbox@init
+   \spx@boxes@fcolorbox@setuphook
    % reserve space to shadow if on left
    \ifspx@boxes@withshadow
      \ifdim\spx@boxes@shadow@xoffset<\z@\kern-\spx@boxes@shadow@xoffset\fi