\documentclass[12pt,portrait]{article}

\usepackage{graphicx}
%\usepackage{blindtext}
\usepackage{hyperref} %--- per i link
\usepackage{multicol} %------ per formattare pagine a più colonne
\usepackage[T1]{fontenc}
\usepackage{tcolorbox} %--- per le caselle di testo I pagina
\usepackage[percent]{overpic}
%------------------------------------
\setlength\textwidth{267mm}
\setlength\paperwidth{300mm}
\setlength\oddsidemargin{-1cm}
%-------------------------------
\usepackage{ebgaramond-maths}%----- uso font garamond
\usepackage[T1]{fontenc}%----- uso font garamond
%\pagestyle{empty}
\usepackage[margin=0pt]{geometry}
\usepackage{showframe}
%------ set colori del link
\hypersetup{
    colorlinks=true,
    linkcolor=black,
    filecolor=magenta,
    urlcolor=cyan,
    pdftitle={Overleaf Example},
    pdfpagemode=FullScreen,
    }

 %----- dimensione della pagina ------
 \geometry{
 a3paper,
 total={297mm,420mm},
 left=15mm,
 top=15mm,
 right=15mm,
 bottom=0mm,
 }


\tcbset{colback=white!5!!,colframe=red!15!white!60!,size=small,
fonttitle=\bfseries,width=0.333\textwidth,box align=top,height=7cm,nobeforeafter}

\begin{document}
%----  inserimento banner --------
    \noindent\includegraphics [height=40mm,width=267mm]{pannello_blu_corto.png}

        \nointerlineskip
      \noindent\includegraphics[height=10mm,width=267mm]{filo_celeste_basso.png}



\noindent
%------ I box ---------------
\nointerlineskip
   \begin{tcolorbox}[adjusted title=\hyperlink{1_1}{bla bla bla},halign=justify]
bla bla bla bla bla
    \end{tcolorbox} %------fine I box --------
    \begin{tcolorbox}[adjusted title=\hyperlink{1_1}{xyzxyz xyz xyz xy},halign=justify]
xyz xyz xyz xyz xyz xyz
        \end{tcolorbox}
  \begin{tcolorbox}[adjusted title=\hyperlink{1_1}{xyzxyz xyz xyz xy},halign=justify]
xyz xyz xyz xyz xyz xyz
    \end{tcolorbox}\\
    \begin{tcolorbox}[adjusted title=left,halign=left]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}\\
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}\\
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}\\
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
\begin{tcolorbox}[adjusted title=right,halign upper=right]
This is a demonstration text for showing how line breaking works.
\end{tcolorbox}
   \newpage
    \begin{multicols}{3}
\hypertarget{1_1}{E’ fresco di stampa} bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
    \end{multicols}
\end{document}