Hcfyk

Is it possible to add double frame in a tcolorbox? Actually I am trying to design a chapter using titlesec and tcolorbox which has two borders. Inner border colour will be white ( same as the page colour ) and the outer border colour will be cyan ( same as the box background colour) something like this.

This is the code which I was trying :

usepackage[explicit]{titlesec}

usepackage[many]{tcolorbox}

definecolor{myCyan}{HTML}{13C39D}

titleformat{chapter}[display]

{sffamilybfseriesHugefilcenter}

{}

{0pt}

{%

    begin{tcolorbox}[

        enhanced,

        colback = myCyan,

        fontupper=color{white},

        boxrule=0pt,

        colframe=black!70!white,

        arc=0pt,

        outer arc=0pt,

        top=20pt,

        bottom=20pt,

        left=20pt,

        right=20pt,

        ]

        begin{center}

            #1

        end{center}

    end{tcolorbox}%

}



titlespacing*{chapter}{0pt}{0cm}{0cm}

This may be a start. The idea is to nest tcolorboxes.

documentclass{article}

usepackage{tcolorbox}

begin{document}

begin{tcolorbox}[

    colback=green!50!blue,

    colframe=green!50!blue,

    left=1.5pt,right=1.5pt,top=1.5pt,bottom=-1.5pt,

    sharp corners,

    boxsep=0pt

]

begin{tcolorbox}[

    colback=green!50!blue,

    colframe=white,

    leftrule=1.5pt,rightrule=1.5pt,toprule=1.5pt,bottomrule=1.5pt,

    sharp corners,

    fontupper=color{white}sffamilybfseriesLargecentering

]

Android tutorial

end{tcolorbox}%

end{tcolorbox}

end{document}

Now let's customize our chapter with it.

documentclass{book}

usepackage[explicit]{titlesec}

usepackage[many]{tcolorbox}

definecolor{myCyan}{HTML}{13C39D}

titleformat{chapter}[display]

{sffamilybfseriesHugefilcenter}

{}

{0pt}

{%

begin{tcolorbox}[

    colback=myCyan,

    colframe=myCyan,

    left=1.5pt,right=1.5pt,top=1.5pt,bottom=-1.5pt,

    sharp corners,

    boxsep=0pt

]

begin{tcolorbox}[

    colback=myCyan,

    colframe=white,

    leftrule=1.5pt,rightrule=1.5pt,toprule=1.5pt,bottomrule=1.5pt,

    sharp corners,

    fontupper=color{white}sffamilybfseriesHugecentering

]

thechapter. #1

end{tcolorbox}%

end{tcolorbox}%

}



titlespacing*{chapter}{0pt}{0cm}{0cm}

usepackage{lipsum}

begin{document}

chapter{Lorem lipsum}



lipsum[1]

end{document}

There's no need for nested tcolorboxes, you could use an enhanced box with an additional borderline:

documentclass{book}

usepackage[explicit]{titlesec}

usepackage[many]{tcolorbox}

definecolor{myCyan}{HTML}{13C39D}

titleformat{chapter}[display]

{sffamilybfseriesHugefilcenter}

{}

{0pt}

{%

begin{tcolorbox}[

    enhanced,

    colback=myCyan,

    colframe=myCyan,

    boxsep=5pt,

    sharp corners,

    borderline={1.5pt}{3pt}{white},

    colupper=white,

    fontupper=sffamilybfseriesHuge,

    halign upper=center

]

thechapter. #1

end{tcolorbox}%

}



titlespacing*{chapter}{0pt}{0cm}{0cm}

usepackage{lipsum}

begin{document}

chapter{Lorem lipsum}



lipsum[1]

end{document}