Generating grid in a box

Question

I'm using the following preamble

\documentclass[10pt]{article}

\usepackage{graphicx}
\usepackage{colortbl}
\usepackage[table]{xcolor}
\usepackage[many]{tcolorbox}

\usepackage{XCharter}
\usepackage[T1]{fontenc}

\newtcolorbox{learng}{
  breakable,
  enhanced,
  arc=0pt,
  outer arc=0pt,
  colframe=titlegrammar,
  colback=titlegrammar!03,
  overlay unbroken and first={
    \node[
      draw=titlegrammar,
      fill=titlegrammar,
      rotate=270,
      anchor=north west,
      text=white,
      font=\bfseries
    ]
    at (frame.north west)
    {LEARN THIS!};
  }
}

\definecolor{titlegrammar}{RGB}{255,128,0}

\begin{document}

\begin{learng}
text goes here
\end{learng}

\end{document}

This generates a similar box:

If you look closely to the picture, you'll see some kind of grid yielded. I'd like to replicate that result. Is it possible?

---

After having my question answered, I made some modifications and the result is as follows:

Answer 1

Use the underlay={...} option with \fill[...] and a \filldraw for the grid. I have used some opacity value to reduce the intensity of the colour, but this depends on personal views, of course.

Since tcolorbox uses TikZ in the background, basically all TikZ operations are possible.

The white lines are exaggerated here on purpose for demonstration only!

Basically, only the colframe colour needs to be specified, all other values are using tcbcol@frame then.

\documentclass[10pt]{article}

\usepackage{graphicx}
\usepackage{colortbl}
\usepackage[table]{xcolor}
\usepackage[most]{tcolorbox}

\usepackage{blindtext}
\usepackage{XCharter}
\usepackage[T1]{fontenc}

\definecolor{titlegrammar}{RGB}{255,128,0}
\newtcolorbox{learng}{
  breakable,
  enhanced,
  arc=0pt,
  outer arc=0pt,
  colframe=titlegrammar,
  colback=tcbcol@frame!03,
  overlay unbroken and first={
    \node[
      draw=tcbcol@frame,
      fill=tcbcol@frame,
      rotate=270,
      anchor=north west,
      text=white,
      font=\bfseries
    ]
    at (frame.north west)
    {LEARN THIS!};
  },
  underlay={\begin{tcbclipinterior}
      \fill[tcbcol@frame,opacity=0.4] (interior.south west) rectangle (interior.north east);
      \filldraw[help lines,step=5mm,line width=2pt,white,shift={(interior.north west)}]
      (interior.south west) grid (interior.north east);
    \end{tcbclipinterior}}
}


\begin{document}

\begin{learng}
\blindtext
\end{learng}
\end{document}