tcolorbox com bicolor, mas apenas o quadro direito delineado

Question

Como eu seria capaz de criar o seguinte usando um tcolorbox?

Sempre que tento, o melhor que consigo é o seguinte:

MWE:

    \documentclass[12pt]{article}

\usepackage[many]{tcolorbox}
\usepackage{tikz}
\usepackage[margin=2cm,includefoot,bottom=2.55cm,top=2.025cm,headsep=0.5cm,footskip=0.65cm]{geometry}

\definecolor{myblue}{RGB}{0,46,142}
\newtcolorbox[auto counter]{mytheorem}[1][]{
  enhanced jigsaw,colback=white,colframe=myblue,coltitle=myblue,
  fonttitle=\bfseries,
  sharp corners,
  detach title,
  leftrule=18mm,
  underlay unbroken and first={\node[above,text=white,font=\bfseries,align=center]
    at ([xshift=-9mm,yshift=0mm]interior.west) {\thetcbcounter};},
  breakable,pad at break=1mm,
  #1,
  code={\ifdefempty{\tcbtitletext}{}{\tcbset{before upper={\tcbtitle\par\medskip}}}},
}

\begin{document}\raggedright

  \begin{mytheorem}[title=Important Note]
    Important content. A body remains in a state of rest or continuous uniform motion unless acted on by an unbalanced external force.
      \begin{align*}
        45x^2-4x  & =75x
        \end{align*}
  \end{mytheorem}


\end{document}

Também estou me perguntando o que seria necessário para ter o número da caixa no centro de sua coluna ou, alternativamente, no topo da coluna alinhado com o título.

Muito obrigado

Answer 1

Em vez de aumentar a largura da regra, eu aumentaria a margem esquerda e colocaria o número lá.

\documentclass[12pt]{article}

\usepackage[many]{tcolorbox}
\usepackage[%
    margin=2cm,
    includefoot,
    bottom=2.55cm,
    top=2.025cm,
    headsep=0.5cm,
    footskip=0.65cm
]{geometry}

\definecolor{myblue}{RGB}{0,46,142}

\newtcolorbox[auto counter]{mytheorem}[1][]{%
    enhanced jigsaw,
    colback=white,
    colframe=myblue,
    coltitle=myblue,
    fonttitle=\bfseries,
    sharp corners,
    detach title,
    enlarge left by=18mm,
    width=\linewidth-18mm,
    underlay unbroken and first={%
       \node[above,text=myblue,font=\bfseries,align=center] at ([xshift=-.5\textwidth,yshift=-7mm]interior.north) {\thetcbcounter};
    },
    breakable,
    pad at break=1mm,
    #1,
    code={\ifdefempty{\tcbtitletext}{}{\tcbset{before upper={\tcbtitle\par\medskip}}}},
}

\begin{document}\raggedright

  \begin{mytheorem}[title=Important Note]
    Important content. A body remains in a state of rest or continuous uniform motion unless acted on by an unbalanced external force.
      \begin{align*}
        45x^2-4x  & =75x
        \end{align*}
  \end{mytheorem}


\end{document}