diff --git a/de.sty b/de.sty
index 98a3700..68d6e15 100644
--- a/de.sty
+++ b/de.sty
@@ -1,4 +1,4 @@
-\documentclass[a4paper, 12pt]{article}
+\documentclass[a4paper, 12pt, dvipsnames]{article}
 \usepackage[utf8]{inputenc}
 \usepackage[T2A,T1]{fontenc}
 \usepackage[english, ukrainian]{babel}
@@ -7,6 +7,8 @@
 \usepackage{geometry}
 \usepackage{graphicx}
 
+% \input{th.sty}
+
 \usepackage{eso-pic}
 \newcommand\BackgroundPic{\put(0,0){\parbox[b][\paperheight]{\paperwidth}{\includegraphics[width=\paperwidth, height=\paperheight]{background.png}}}}
 
@@ -21,19 +23,19 @@
 
 \usepackage{xcolor, float, multirow, multicol, hyperref}
 \definecolor{cover}{RGB}{191,0,0}
-\hypersetup{unicode=true, colorlinks=true, linktoc=all, linkcolor=red}
+\hypersetup{unicode=true, colorlinks=true, linktoc=all, linkcolor=Red}
 
-\usepackage{amsthm}
-\newtheorem{theorem}{Теорема}[section]
-\newtheorem{lemma}{Лема}[section]
-\theoremstyle{definition}
-\newtheorem*{definition}{Визначення}
-\newtheorem{problem}{Задача}[subsection]
-\newtheorem*{example*}{Приклад}
-\newtheorem{example}[problem]{Приклад}
-\newtheorem{property}{Властивість}
-\newtheorem*{solution}{Розв'язок}
-\newtheorem*{remark}{Зауваження}
+% \usepackage{amsthm}
+% \newtheorem{theorem}{Теорема}[section]
+% \newtheorem{lemma}{Лема}[section]
+% \theoremstyle{definition}
+% \newtheorem*{definition}{Визначення}
+% \newtheorem{problem}{Задача}[subsection]
+% \newtheorem*{example*}{Приклад}
+% \newtheorem{example}[problem]{Приклад}
+% \newtheorem{property}{Властивість}
+% \newtheorem*{solution}{Розв'язок}
+% \newtheorem*{remark}{Зауваження}
 
 \renewcommand{\phi}{\varphi}
 \renewcommand{\epsilon}{\varepsilon}
@@ -72,4 +74,3 @@
 	\fi%
 }
 \makeatother
-
diff --git a/main.tex b/main.tex
index 742f22c..0de87ea 100644
--- a/main.tex
+++ b/main.tex
@@ -1,6 +1,5 @@
 % cd ..\..\Users\NikitaSkybytskyi\Desktop\differential-equations
 % pdflatex main.tex && cls && pdflatex main.tex && cls && pdflatex main.tex && del main.toc, main.log, main.aux, main.out && start main.pdf
-
 \input{de.sty}
 
 \begin{document}
diff --git a/subsubsection-1-3-2.tex b/subsubsection-1-3-2.tex
index b005a81..a4c93f0 100644
--- a/subsubsection-1-3-2.tex
+++ b/subsubsection-1-3-2.tex
@@ -9,7 +9,7 @@
 
 Зробимо заміну: 
 \begin{equation*}
-	y^{1-m} = z, \quad (1 - m) y^{-m} \frac{\diff y}{\diff x} = \diff z.
+	y^{1-m} = z, \quad (1 - m) y^{-m} \frac{\diff y}{\diff x} = \frac{\diff z}{\diff x}. % thanks to Denys Chergykalo for a valuable suggestion here
 \end{equation*}
 
 Підставивши в рівняння, отримаємо
diff --git a/th.sty b/th.sty
new file mode 100644
index 0000000..3e99131
--- /dev/null
+++ b/th.sty
@@ -0,0 +1,104 @@
+\usepackage{amsthm}
+\usepackage[dvipsnames]{xcolor}
+\usepackage{thmtools}
+\usepackage[framemethod=TikZ]{mdframed}
+
+\theoremstyle{definition}
+\mdfdefinestyle{mdbluebox}{%
+	roundcorner = 10pt,
+	linewidth=1pt,
+	skipabove=12pt,
+	innerbottommargin=9pt,
+	skipbelow=2pt,
+	nobreak=true,
+	linecolor=blue,
+	backgroundcolor=TealBlue!5,
+}
+\declaretheoremstyle[
+	headfont=\sffamily\bfseries\color{MidnightBlue},
+	mdframed={style=mdbluebox},
+	headpunct={\\[3pt]},
+	postheadspace={0pt}
+]{thmbluebox}
+
+\mdfdefinestyle{mdredbox}{%
+	linewidth=0.5pt,
+	skipabove=12pt,
+	frametitleaboveskip=5pt,
+	frametitlebelowskip=0pt,
+	skipbelow=2pt,
+	frametitlefont=\bfseries,
+	innertopmargin=4pt,
+	innerbottommargin=8pt,
+	nobreak=true,
+	linecolor=RawSienna,
+	backgroundcolor=Salmon!5,
+}
+\declaretheoremstyle[
+	headfont=\bfseries\color{RawSienna},
+	mdframed={style=mdredbox},
+	headpunct={\\[3pt]},
+	postheadspace={0pt},
+]{thmredbox}
+
+\declaretheorem[%
+style=thmbluebox,name=Теорема,numberwithin=section]{theorem}
+\declaretheorem[style=thmbluebox,name=Лема,sibling=theorem]{lemma}
+\declaretheorem[style=thmbluebox,name=Твердження,sibling=theorem]{proposition}
+\declaretheorem[style=thmbluebox,name=Наслідок,sibling=theorem]{corollary}
+\declaretheorem[style=thmredbox,name=Приклад,sibling=theorem]{example}
+
+\mdfdefinestyle{mdgreenbox}{%
+	skipabove=8pt,
+	linewidth=2pt,
+	rightline=false,
+	leftline=true,
+	topline=false,
+	bottomline=false,
+	linecolor=ForestGreen,
+	backgroundcolor=ForestGreen!5,
+}
+\declaretheoremstyle[
+	headfont=\bfseries\sffamily\color{ForestGreen!70!black},
+	bodyfont=\normalfont,
+	spaceabove=2pt,
+	spacebelow=1pt,
+	mdframed={style=mdgreenbox},
+	headpunct={ --- },
+]{thmgreenbox}
+
+\mdfdefinestyle{mdblackbox}{%
+	skipabove=8pt,
+	linewidth=3pt,
+	rightline=false,
+	leftline=true,
+	topline=false,
+	bottomline=false,
+	linecolor=black,
+	backgroundcolor=RedViolet!5!gray!5,
+}
+\declaretheoremstyle[
+	headfont=\bfseries,
+	bodyfont=\normalfont\small,
+	spaceabove=0pt,
+	spacebelow=0pt,
+	mdframed={style=mdblackbox}
+]{thmblackbox}
+
+% \theoremstyle{theorem}
+\declaretheorem[name=Запитання,sibling=theorem,style=thmblackbox]{ques}
+\declaretheorem[name=Вправа,sibling=theorem,style=thmblackbox]{exercise}
+\declaretheorem[name=Зауваження,sibling=theorem,style=thmgreenbox]{remark}
+
+\theoremstyle{definition}
+\newtheorem{claim}[theorem]{Твердження}
+\newtheorem{definition}[theorem]{Визначення}
+\newtheorem{fact}[theorem]{Факт}
+
+\newtheorem{problem}{Задача}[section]
+\renewcommand{\theproblem}{\thesection\Alph{problem}}
+\newtheorem{sproblem}[problem]{Задача}
+\newtheorem{dproblem}[problem]{Задача}
+\renewcommand{\thesproblem}{\theproblem$^{\star}$}
+\renewcommand{\thedproblem}{\theproblem$^{\dagger}$}
+\newcommand{\listhack}{$\empty$\vspace{-2em}}
\ No newline at end of file