A basic LaTeX template because I'm changing it too much to make it a .cls file

template.tex

% thx @jix_ for sharing their fonts
% compiles out of the box on https://tectonic-typesetting.github.io/ but may work
% on other LaTeX distros
\documentclass[a4paper,12pt,headings=standardclasses]{scrartcl}
\usepackage{mathpazo}
\usepackage{fontspec}
\setmainfont{TeX Gyre Pagella}
\setkomafont{disposition}{}\RedeclareSectionCommands[font=\bfseries]{paragraph}

\usepackage{tikz,tkz-euclide}
\usepackage{amssymb}
\usepackage[polish]{babel}
\usetkzobj{all}
\usetikzlibrary{graphs}

\usepackage{amsmath,amsthm,gensymb,hyperref,graphicx,geometry,multicol}
\usepackage[shortlabels]{enumitem}
\geometry{top=1.5cm,bottom=2.5cm,left=2cm,right=2cm}

\newcommand\NN{\mathbb N}
\newcommand\RR{\mathbb R}
\newcommand\QQ{\mathbb Q}
\newcommand\ZZ{\mathbb Z}
\newcommand\OO{\mathcal O}
\newcommand\qq[1]{\stackrel{?}{#1}} % e.g. \qq\geq
\parindent=0pt
\parskip=6pt

\newtheorem{theorem}{Twierdzenie}
\newtheorem{problem}{Zadanie}
\newtheorem{lemma}{Lemat}[problem]
\theoremstyle{definition}
\newtheorem{defn}{Definicja}

\begin{document}