diff --git a/beamercolorthemeaptero.sty b/beamercolorthemeaptero.sty
index 557ea2c..0d2ae5f 100644
--- a/beamercolorthemeaptero.sty
+++ b/beamercolorthemeaptero.sty
@@ -9,12 +9,6 @@
 
 \ProvidesPackage{beamercolorthemeaptero}[2021/02/28 color theme for lines inner and outer beamer theme]
 
-\newif\if@beamer@colors@set
-\DeclareOptionBeamer{noset}{\@beamer@colors@setfalse}
-\DeclareOptionBeamer{set}{\@beamer@colors@settrue}
-\ExecuteOptionsBeamer{set}
-\ProcessOptionsBeamer
-
 % muted colors:
 \definecolor{red}{rgb}{0.753,0.153,0.090}
 \definecolor{orange}{rgb}{0.969,0.502,0.090}
@@ -72,17 +66,11 @@
 \setbeamercolor{block line example middle}{fg=lightgreen}
 \setbeamercolor{block line example bottom}{fg=lightgreen}
 
-\if@beamer@colors@set
-
-  \addtobeamertemplate{proof begin}{%
-    \setbeamercolor{block title}{fg=white, bg=green}
-  }{}
-
-  \addtobeamertemplate{theorem begin}{%
-    \setbeamercolor{block title}{fg=white, bg=orange}
-  }{}
-  
-\fi
+\setbeamercolor{theorem title}{parent={block title}, bg=orange}
+\setbeamercolor{theorem body}{fg=normal text.fg, bg=orange!40}
+\setbeamercolor{theorem line top}{fg=}
+\setbeamercolor{theorem line middle}{fg=orange}
+\setbeamercolor{theorem line bottom}{fg=orange}
 
 \setbeamercolor{section in toc}{parent={normal text}}
 \setbeamercolor{subsection in toc}{parent={normal text}}
diff --git a/beamercolorthemeut.sty b/beamercolorthemeut.sty
index b840332..63eeca4 100644
--- a/beamercolorthemeut.sty
+++ b/beamercolorthemeut.sty
@@ -67,13 +67,11 @@
 \setbeamercolor{block line example middle}{fg=utgreen}
 \setbeamercolor{block line example bottom}{fg=utgreen}
 
-\addtobeamertemplate{proof begin}{%
-  \setbeamercolor{block title}{fg=white, bg=utmagenta}
-}{}
-
-\addtobeamertemplate{theorem begin}{%
-  \setbeamercolor{block title}{fg=white, bg=utorange}
-}{}
+\setbeamercolor{theorem title}{parent={block title}, bg=utorange}
+\setbeamercolor{theorem body}{fg=normal text.fg, bg=utorange!25}
+\setbeamercolor{theorem line top}{fg=}
+\setbeamercolor{theorem line middle}{fg=utorange}
+\setbeamercolor{theorem line bottom}{fg=utorange}
 
 \setbeamercolor{section in toc}{parent={normal text}}
 \setbeamercolor{subsection in toc}{parent={normal text}}
diff --git a/beamerthemelines.sty b/beamerthemelines.sty
index 6826ea5..2d6615d 100644
--- a/beamerthemelines.sty
+++ b/beamerthemelines.sty
@@ -10,10 +10,6 @@
 \RequirePackage{tikz}
 \RequirePackage{xstring}
 
-% pass set/noset option to aptero color theme:
-\DeclareOptionBeamer{set}{\PassOptionsToPackage{set}{beamercolorthemeaptero}}
-\DeclareOptionBeamer{noset}{\PassOptionsToPackage{noset}{beamercolorthemeaptero}}
-
 \newif\if@beamer@footline@author
 \newif\if@beamer@footline@institute
 \newif\if@beamer@footline@date
@@ -346,7 +342,7 @@
 \newcommand{\block@lines@begin}[3]{%
  \par\vskip\medskipamount%
   \usebeamerfont{block title#1}%
-  \IfStrEq{\insertblocktitle}{}{}{%
+  \IfStrEq{\insertblocktitle}{}{}{%    % IfStrEq does not work for theorems!
     \ifbeamercolorempty[fg]{block line#1 top}{}{%
       \nointerlineskip
       \begin{beamercolorbox}[wd=\columnwidth,hd=#2]{block line#1 top}
@@ -405,6 +401,61 @@
 \setbeamertemplate{block example end}[lines]{0.5pt}
 
 
+%%%%% theorem environments (theorem, corollary, fact, lemma, definition, example):
+
+\newcommand{\theorem@lines@begin}[3]{%
+ \par\vskip\medskipamount%
+  \usebeamerfont{#1 title}%
+  \ifbeamercolorempty[fg]{#1 line top}{}{%
+    \nointerlineskip
+    \begin{beamercolorbox}[wd=\columnwidth,hd=#2]{#1 line top}
+      \rule{\columnwidth}{#2}
+    \end{beamercolorbox}
+    \nointerlineskip%
+  }
+  \begin{beamercolorbox}[wd=\columnwidth,ht=2.4ex,dp=0.9ex,leftskip=2mm,rightskip=2mm]{#1 title}
+    \strut \insertblocktitle
+  \end{beamercolorbox}
+  \nointerlineskip
+  \ifbeamercolorempty[fg]{#1 line middle}{}{%
+    \begin{beamercolorbox}[wd=\columnwidth,hd=#3]{#1 line middle}
+      \rule{\columnwidth}{#3}
+    \end{beamercolorbox}
+    \nointerlineskip}%
+  \usebeamerfont{#1 body}%
+  \begin{beamercolorbox}[wd=\columnwidth,colsep=2mm]{#1 body}
+ }
+
+\newcommand{\theorem@lines@end}[2]{%
+    \vspace{-0.4ex}%
+  \end{beamercolorbox}%
+  \ifbeamercolorempty[fg]{#1 line bottom}{}{%
+    \nointerlineskip
+    \begin{beamercolorbox}[wd=\columnwidth,hd=#2]{#1 line bottom}
+      \rule{\columnwidth}{#2}
+    \end{beamercolorbox}
+  }%
+}
+
+\newenvironment<>{theoremblock}[1]{%
+  \begin{actionenv}#2%
+    \def\insertblocktitle{#1}%
+    \par%
+    \usebeamertemplate{block theorem begin}}
+  {\par%
+    \usebeamertemplate{block theorem end}%
+  \end{actionenv}}
+
+\renewcommand{\inserttheoremblockenv}{theoremblock}
+\renewcommand{\inserttheoremheadfont}{}
+
+\defbeamertemplate{block theorem begin}{lines}[2]{\theorem@lines@begin{theorem}{#1}{#2}}
+\defbeamertemplate{block theorem end}{lines}[1]{\theorem@lines@end{theorem}{#1}}
+
+\setbeamertemplate{block theorem begin}[lines]{0.5pt}{0.5pt}
+\setbeamertemplate{block theorem end}[lines]{0.5pt}
+
+
 %%%%% title page %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 %%%%% title page graphic line:
@@ -663,6 +714,11 @@
 \setbeamerfont{institute}{size=\normalsize}
 \setbeamerfont{date}{size=\tiny}
 
+\setbeamerfont{block title}{size=\normalsize}
+\setbeamerfont{block title alerted}{size=\normalsize}
+\setbeamerfont{block title example}{size=\normalsize}
+\setbeamerfont{theorem title}{size=\normalsize}
+
 \setbeamerfont*{section title}{size=\huge}
 \setbeamerfont*{section name}{size=\huge}
 \setbeamerfont*{subsection title}{size=\Large}
diff --git a/beamerthemeut.sty b/beamerthemeut.sty
index 69e9184..35d661d 100644
--- a/beamerthemeut.sty
+++ b/beamerthemeut.sty
@@ -49,14 +49,17 @@
 \setbeamertemplate{enumerate item}[arabic]  % default, circle, square, ball, alph, Alph, arabic, roman, Roman
 \setbeamertemplate{enumerate subitem}[alph] % default, circle, square, ball, alph, arabic, roman
 
-\setbeamertemplate{block begin}[lines]{1pt}{1pt} % default, rounded, lines
-\setbeamertemplate{block end}[lines]{1pt}
+\setbeamertemplate{block begin}[lines]{0.75pt}{0.75pt} % default, rounded, lines
+\setbeamertemplate{block end}[lines]{0.75pt}
 
-\setbeamertemplate{block alerted begin}[lines]{1pt}{1pt} % default, rounded, lines
-\setbeamertemplate{block alerted end}[lines]{1pt}
+\setbeamertemplate{block alerted begin}[lines]{0.75pt}{0.75pt} % default, rounded, lines
+\setbeamertemplate{block alerted end}[lines]{0.75pt}
 
-\setbeamertemplate{block example begin}[lines]{1pt}{1pt} % default, rounded, lines
-\setbeamertemplate{block example end}[lines]{1pt}
+\setbeamertemplate{block example begin}[lines]{0.75pt}{0.75pt} % default, rounded, lines
+\setbeamertemplate{block example end}[lines]{0.75pt}
+
+\setbeamertemplate{block theorem begin}[lines]{0.75pt}{0.75pt}
+\setbeamertemplate{block theorem end}[lines]{0.75pt}
 
 \setbeamertemplate{title page}[leftlines]          % leftlines, centerlines
 \setbeamertemplate{title page graphic line}[default][1.4ex]
diff --git a/lines-example.tex b/lines-example.tex
index 837b295..6a0f2c8 100644
--- a/lines-example.tex
+++ b/lines-example.tex
@@ -259,13 +259,25 @@
 \end{frame}
 
 \begin{frame}{Theorems}
-  Not supported yet.
-  % \begin{definition}
-  %   Definition block with content: \texttt{definition} environment.
-  % \end{definition}
-  % \begin{proof}
-  %   Proof block with content: \texttt{proof} environment.
-  % \end{proof}
+  \begin{theorem}
+    \texttt{theorem} environment.
+  \end{theorem}
+  \begin{definition}
+    Definition block with content: \texttt{definition} environment.\\[1ex]
+    All theorem environments get the same color and font:
+    \begin{itemize}
+    \item \texttt{theorem title}
+    \item \texttt{theorem body}
+    \item \texttt{theorem line top/middle/bottom}
+    \end{itemize}
+  \end{definition}
+  %\begin{example}
+  %  Example block with content: \texttt{example} environment.
+  %\end{example}
+  \begin{proof}
+    Proof block with content: \texttt{proof} environment.\\
+    Same colors and fonts as the \texttt{block} environment.
+  \end{proof}
 \end{frame}
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
diff --git a/ut-example.tex b/ut-example.tex
index 0107443..9dd7876 100644
--- a/ut-example.tex
+++ b/ut-example.tex
@@ -154,6 +154,7 @@
 \end{frame}
 
 \begin{frame}{Block environments with title}
+  ... add structure and color to a slide --- use them with care:
   \begin{block}{Some block}
     \texttt{block} environment with title as argument.
   \end{block}
@@ -166,6 +167,7 @@
 \end{frame}
 
 \begin{frame}{Block environments without title}
+  ... add color to a slide in a more subtle way:
   \begin{block}{}
     Block with empty title.\\
     And just some text.
@@ -181,13 +183,25 @@
 \end{frame}
 
 \begin{frame}{Theorems}
-  Not supported yet.
-  % \begin{definition}
-  %   Definition block with content: \texttt{definition} environment.
-  % \end{definition}
-  % \begin{proof}
-  %   Proof block with content: \texttt{proof} environment.
-  % \end{proof}
+  \begin{theorem}
+    \texttt{theorem} environment.
+  \end{theorem}
+  \begin{definition}
+    Definition block with content: \texttt{definition} environment.\\[1ex]
+    All theorem environments get the same color and font:
+    \begin{itemize}
+    \item \texttt{theorem title}
+    \item \texttt{theorem body}
+    \item \texttt{theorem line top/middle/bottom}
+    \end{itemize}
+  \end{definition}
+  %\begin{example}
+  %  Example block with content: \texttt{example} environment.
+  %\end{example}
+  \begin{proof}
+    Proof block with content: \texttt{proof} environment.
+    Same colors and fonts as the \texttt{block} environment.
+  \end{proof}
 \end{frame}
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%