# caption for pictures and formulas on the top left side in a only right sided document

I want a document that has only right pages and always the broader margin on the left side. The caption of pictures and formulas should be at the top left side and align with the text. I know how i make thw first two things but i fail at the last one. I tried these:

KOMA-Script and sidenotes : how to format side (margin) caption and its caption label?

captionsetup for margin caption

However i always end up with captions that are either on the left side or broken ones.

MWE from here by ebosi: KOMA-Script and sidenotes : how to format side (margin) caption and its caption label?

this kind of works. But when i change it to oneside, everything is on the right side. I want it on the left side

Starting with the linked MWE, you just need \reversemarginpar.

\documentclass[oneside]{scrartcl}
%\usepackage[T1]{fontenc}% not with my editor
\usepackage{lipsum}
\usepackage{graphicx}
\usepackage{sidenotes}

\DeclareCaptionStyle{sidecaption}{labelfont={sc,bf},justification=raggedright}
\reversemarginpar
\addtolength{\textwidth}{\dimexpr \marginparsep+\marginparwidth}% use marginpar area for text
% Do NOT use \recalctypearea
\begin{document}
\lipsum
\begin{figure}[htb]
\sidecaption[][-2\baselineskip]{This is my caption}
\includegraphics[width=\textwidth, height=20em]{example-image-a}
\end{figure}
\lipsum
\end{document}