How can I put a minipage that fits to the actual line width inside of a TikZ Node?

Question

Question

I would like to put a minipage environment inside of a tikz node. I know this is done already with the align=left command, but if you set a minimum width of the node to \linewidth, then the text is left aligned, but surrounded by white space padding (depending on how much text you include)

Problem

When I set the width of the minipage environment to \linewidth, minipage grabs the width of the line on a page instead of the width of the node.

Sample Code

\newcommand{\warning}[1]{%
% Define box and box title style
\tikzstyle{mybox} = [align=left,draw=red, very thick,
    rectangle, rounded corners, inner sep=10pt, inner ysep=10pt,maximum width=\linewidth]
\tikzstyle{fancytitle} =[fill=red, text=white,rounded corners]
\begin{tikzpicture}
    \node [mybox] (box){%
        \begin{minipage}{1\textwidth}
        #1
        \end{minipage}
        };
    \node[fancytitle, right=10pt] at (box.north west) {Note:};
\end{tikzpicture}
}%

Adapted code from http://www.texample.net/tikz/examples/boxes-with-text-and-math/

Answer 1

Like this?

 \documentclass{article}
\usepackage{tikz,lipsum,showframe}
\tikzset{mybox/.style = {text width=\dimexpr\linewidth-20pt-\pgflinewidth\relax,align=justify,draw=red,
                very thick, rectangle, rounded corners, inner sep=10pt, inner ysep=10pt},
        fancytitle/.style ={fill=red, text=white,rounded corners}
}
\begin{document}
\noindent
\begin{tikzpicture}
    \node [mybox] (box){%
        \lipsum[1]
        };
    \node[fancytitle, right=10pt] at (box.north west) {Note:};
\end{tikzpicture}
\end{document}

With an explicit minipage as requested:

\documentclass{article}
\usepackage{tikz,lipsum,showframe}
\tikzset{mybox/.style = {align=center,draw=red,
                very thick, rectangle, rounded corners, inner sep=10pt, inner ysep=10pt},
        fancytitle/.style ={fill=red, text=white,rounded corners}
}
\begin{document}
\noindent
\begin{tikzpicture}
    \node [mybox] (box){%
        \begin{minipage}{\dimexpr\linewidth-20pt-\pgflinewidth\relax}
          \lipsum[1]
        \end{minipage}%
        };
    \node[fancytitle, right=10pt] at (box.north west) {Note:};
\end{tikzpicture}
\end{document}