How do I position the x and y labels simultaneously for adjacent tikz plots?

Question

I have code that produces two tikz plots, one above the other. It uses pgfplotset to define a custom style for the axes, which is applied to both plots.

I'm trying to change the position of the x axis label for each axis within the custom style to put the label immediately below the axis. I know I could do this manually in each plot with \coordinate, but I'd like to avoid manually doing this if at all possible. Following this question and answer, I tried adding this code to the style:

every axis x label/.style={at={(current axis.right of origin)},anchor=west},

Adding this option makes the x label only show in the first plot, not the second. What am I doing wrong?

Code:

\documentclass[12pt,a4paper]{article}

\usepackage{float}
\usepackage[margin=1cm]{geometry}
\usepackage{pgfplots}
\pgfplotsset{compat=1.13}  
\pagestyle{empty}

\pgfplotsset{customaxisstyle/.style={%
        width=18cm, height=10cm,
        title={}, xlabel={$s$}, ylabel={}, xticklabels={,,}, yticklabels={,,}, axis lines=middle,   
        xmin=0, xmax=10,
        ymin=0, ymax=5,
        domain=0:10, samples=100}}

\pgfplotsset{customlinestyle1/.style={black, thick}}
\pgfplotsset{customlinestyle2/.style={blue, line width=1mm}}

\begin{document}
\begin{figure}[H]
\begin{tikzpicture}

\begin{scope}
\begin{axis}[customaxisstyle,title={Top plot}]
\addplot[customlinestyle1] {1.8 - 0.2*x};
\addplot[customlinestyle1] {3.0 - 0.4*x};
\addplot[customlinestyle1] {2.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.8*x};
\addplot[customlinestyle1] {5.0 - 1.2*x};
\end{axis}
\end{scope}

\begin{scope}[yshift=-10cm]
\begin{axis}[customaxisstyle, title={Bottom plot}]
\addplot[red, very thick] { 2 * sin(deg(0.5*x + 6)) + 2.5 };
\end{axis}
\end{scope}

\end{tikzpicture}
\end{figure}
\end{document}

Output:

Answer 1

You can use e.g.

 xlabel style ={at={(xticklabel cs:1,0)},anchor=east,inner sep=1pt,}

as in

\documentclass[12pt,a4paper]{article}

\usepackage{float}
\usepackage[margin=1cm]{geometry}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}  
\pagestyle{empty}

\pgfplotsset{customaxisstyle/.style={%
        width=18cm, height=10cm,
        title={}, xlabel={$s$}, ylabel={}, xticklabels={,,}, yticklabels={,,}, axis lines=middle,   
        xlabel style ={at={(xticklabel cs:1,0)},anchor=east,inner sep=1pt,},
        xmin=0, xmax=10,
        ymin=0, ymax=5,
        domain=0:10, samples=100}}

\pgfplotsset{customlinestyle1/.style={black, thick}}
\pgfplotsset{customlinestyle2/.style={blue, line width=1mm}}

\begin{document}
\begin{figure}[H]
\begin{tikzpicture}

\begin{scope}
\begin{axis}[customaxisstyle,title={Top plot}]
\addplot[customlinestyle1] {1.8 - 0.2*x};
\addplot[customlinestyle1] {3.0 - 0.4*x};
\addplot[customlinestyle1] {2.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.8*x};
\addplot[customlinestyle1] {5.0 - 1.2*x};
\end{axis}
\end{scope}

\begin{scope}[yshift=-10cm]
\begin{axis}[customaxisstyle, title={Bottom plot}]
\addplot[red, very thick] { 2 * sin(deg(0.5*x + 6)) + 2.5 };
\end{axis}
\end{scope}

\end{tikzpicture}
\end{figure}
\end{document}

You could get rid of the scopes and manually adjusted yshift by using either groupplots or just a matrix.

\documentclass[12pt,a4paper]{article}

\usepackage{float}
\usepackage[margin=1cm]{geometry}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}  
\pagestyle{empty}

\pgfplotsset{customaxisstyle/.style={%
        width=18cm, height=10cm,
        title={}, xlabel={$s$}, ylabel={}, xticklabels={,,}, yticklabels={,,}, axis lines=middle,   
        xlabel style ={at={(xticklabel cs:1,0)},anchor=east,inner sep=1pt,},
        xmin=0, xmax=10,
        ymin=0, ymax=5,
        domain=0:10, samples=100}}

\pgfplotsset{customlinestyle1/.style={black, thick}}
\pgfplotsset{customlinestyle2/.style={blue, line width=1mm}}

\begin{document}
\begin{figure}[H]
\begin{tikzpicture}
\matrix{
\begin{axis}[customaxisstyle,title={Top plot}]
\addplot[customlinestyle1] {1.8 - 0.2*x};
\addplot[customlinestyle1] {3.0 - 0.4*x};
\addplot[customlinestyle1] {2.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.6*x};
\addplot[customlinestyle1] {3.8 - 0.8*x};
\addplot[customlinestyle1] {5.0 - 1.2*x};
\end{axis}\\
\begin{axis}[customaxisstyle, title={Bottom plot}]
\addplot[red, very thick] { 2 * sin(deg(0.5*x + 6)) + 2.5 };
\end{axis}\\
};
\end{tikzpicture}
\end{figure}
\end{document}