How to get equation number outside of the tcolorbox?

Question

\documentclass{article}
\usepackage{mathtools,amsfonts,amsmath,amssymb,amsthm}
\usepackage[most]{tcolorbox}
\begin{document}

\begin{tcolorbox}[enhanced,boxrule = 1pt,
         colframe = myLColor,
         colback = red!80!black,
         sharp corners,
         rounded corners = southeast,
         rounded corners = northeast,
         rounded corners = southwest,
         rounded corners = northwest,
         arc is angular,
         arc = 3mm,
         coltext = white,attach boxed title to top center={xshift=3mm,yshift*=-\tcboxedtitleheight/2},
  boxed title style={
    colback=blue,
    colframe=blue,
    arc=3mm,
    outer arc=3mm,
    boxrule=0mm,
    boxsep=0mm
  },title=Lots of equations]
Let us consider
\begin{align}
    f&=ma\\
    T_{\mu\nu}&=G_{\mu\nu}
\end{align}
  \end{tcolorbox}

  \end{document}

Is there a way to have this box contains everything but not the equation numbers. I would like the equation numbers to be outside of the tcolorbox but everything else inside the box.

Is it possible to do so?

Answer 1

An extrude right by=<negative length> attempt:

\documentclass{article}
\usepackage{mathtools,amssymb,amsthm}
\usepackage[skins]{tcolorbox}

\colorlet{myLColor}{blue!50}

\newtagform{enforce black}[]{\begingroup\normalcolor(}{)\endgroup}
\usetagform{enforce black}

\begin{document}

\begin{tcolorbox}[title=Normal box]
  Let us consider
  \begin{align}
      f&=ma\\
      T_{\mu\nu}&=G_{\mu\nu}
  \end{align}
\end{tcolorbox}

\begin{tcolorbox}[enhanced,
  boxrule = 1pt,
  colframe = myLColor,
  colback = red!80!black,
  arc is angular,
  arc = 3mm,
  coltext = white,
  attach boxed title to top center={
    xshift=3mm,
    yshift*=-\tcboxedtitleheight/2
  },
  boxed title style={
    colback=blue,
    colframe=blue,
    arc=1.5mm,     % reduced
    outer arc=2mm, % reduced
    boxrule=0mm,
    boxsep=0mm
  },
  title=Lots of equations,
  extrude right by=-1.5cm % << added
]
Let us consider
\begin{align}
    f&=ma\\
    T_{\mu\nu}&=G_{\mu\nu}
\end{align}
\end{tcolorbox}

\end{document}

Note that

• extrude right by doesn't work with tcolorbox breakable boxes, see the marker at the beginning of package manual, sec. 4.15.5 "Box Extrusion".
• Any box content except for equation tags exceeding the right margin of box is still invisible (white on white).