The desired output is as in the second one, but I still want the flexbility of tcolorbox when placing margin notes
My MWE
\documentclass[11pt, a4paper,draft]{book}
\usepackage{fancyhdr}
\pagestyle{empty}
\usepackage[a4paper]{geometry}
% BEGIN_FOLD
% Horizontal
\geometry{textwidth=5cm, marginparsep=3.5mm, marginparwidth=5cm, bindingoffset=0mm, includemp=true}
\geometry{showframe=false, twoside=false}
% END_FOLD
\usepackage[x11names]{xcolor}
\usepackage{marginnote}
% =========== Framed boxes packages ===========
\usepackage{tcolorbox}
\tcbuselibrary{skins,breakable}
% BEGIN_FOLD
\NewDocumentCommand{\sampleText}{}{{\color{gray} Lorem ipsum dolor sit amet, consectetuer adip- iscing elit. Etiam lobortis facilisis sem. Nullam nec mi et neque pharetra sollicitudin. Praesent im- perdiet mi nec ante.}}
\tcbset{MarginNote/.style=%
{
size=minimal,
colframe=white, colback=Ivory1,
opacityframe=0, opacityback=0.75,
box align=base,
nobeforeafter,
width=\linewidth,
}
}%
% END_FOLD
\begin{document}
\smash{\rlap{\rule{\dimexpr \linewidth + \marginparsep + \marginparwidth \relax}{0.1pt}}}%
Text%
\marginnote{%
\tcbox[MarginNote]{\parbox{\linewidth}{The quick brown fox}}%
}
Text
\medskip
\smash{\rlap{\rule{\dimexpr \linewidth + \marginparsep + \marginparwidth \relax}{0.1pt}}}%
Text%
\marginnote{%
\tcbox[MarginNote]{\parbox{\linewidth}{The quick brown fox jumps over the lazy dog}}%
}
Text
\vspace*{2em}
\smash{\rlap{\rule{\dimexpr \linewidth + \marginparsep + \marginparwidth \relax}{0.1pt}}}%
Text%
\marginnote{%
The quick brown fox%
}
Text
\medskip
\smash{\rlap{\rule{\dimexpr \linewidth + \marginparsep + \marginparwidth \relax}{0.1pt}}}%
Text%
\marginnote{%
The quick brown fox jumps over the lazy dog%
}
Text
\end{document}
