Create Beamer-Theorem like boxes using the LaTeX package tcolorbox - version 2.51 (2013/09/16)

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins}

\colorlet{xlightblue}{blue!5}

\newtcolorbox{beamerlikethm}[1]{
  title=#1,
  beamer,
  colback=xlightblue,
  colframe=blue!30,
  fonttitle=\bfseries,
  left=1mm,
  right=1mm,
  top=1mm,
  bottom=1mm,
  middle=1mm
}

\begin{document}

\begin{beamerlikethm}{Theorem (Pythagoras)}
\[ a^2 + b^2 = c^2 \]
\end{beamerlikethm}

\end{document}

Could happen that your box necessitate of being split on different pages. The library breakable of the package deal with this problem.

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{breakable,skins}
\usepackage{lipsum}
\colorlet{xlightblue}{blue!5}
\newtcolorbox{beamerlikethm}[1]
{
title=#1,
beamer, 
colback=xlightblue,
colframe=blue!30,
fonttitle=\bfseries,
left=1mm,
right=1mm,
top=1mm,
bottom=1mm,
middle=1mm,
breakable,
}
\begin{document}
\begin{beamerlikethm}{Theorem (Pythagoras)}
\[ a^2 + b^2 = c^2 \]
\end{beamerlikethm}
\lipsum[1-4]
\begin{beamerlikethm}{Something}
\lipsum[5]
\end{beamerlikethm}
\end{document}

Color transition from title to main body

\documentclass{beamer}
\usetheme{Ilmenau}
\useoutertheme[subsection=false]{smoothbars}

\usepackage{lipsum}

\setbeamertemplate{footline}[default]
\setbeamertemplate{navigation symbols}{}

\definecolor{color3}{rgb}{.4 .4 .4}

\usecolortheme[named = color3]{structure}
\setbeamercolor{frametitle}{fg = white}
\setbeamercolor{background canvas}{bg = black}
\setbeamercolor{normal text}{fg = white}

\makeatletter
\AtBeginDocument{
  {
    \pgfdeclareverticalshading{beamer@belowframetitle}{\the\paperwidth}{%
      color(0ex)=(black);%(global.bg);%
      color(1ex)=(frametitle.bg)
    }
  }
}
\makeatother

\begin{document}
\begin{frame}
    \frametitle{Test}
    \framesubtitle{Test framesubtitle}
    \lipsum[4]
\end{frame}
\end{document}

Transparent foreground watermark

\documentclass{beamer}
\usepackage[printwatermark]{xwatermark}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{lipsum}

\newsavebox\mybox
\savebox\mybox{\tikz[color=red,opacity=0.3]\node{DRAFT};}
\newwatermark*[
  allpages,
  angle=45,
  scale=6,
  xpos=-20,
  ypos=15
]{\usebox\mybox}

\begin{document}

\begin{frame}
\lipsum[4]
\centering
\includegraphics[width=3cm]{example-image-a}
\end{frame}

\end{document}

How Do I Highlight Table Rows in beamer, Piecewise?

\documentclass{beamer}
\usepackage{lmodern}
\usepackage[beamer,customcolors]{hf-tikz}

\tikzset{hl/.style={
    set fill color=red!80!black!40,
    set border color=red!80!black,
  },
}

\begin{document}

\begin{frame}{Title}
\begin{center}
\resizebox{\textwidth}{!}{
\begin{tabular}{lcc|ccc}
\multicolumn{6}{c}{Effect of Mandate on Fertility by Age: Employed Individuals} \\ \hline \hline
 & (1) & (2) & (3) & (4) & (5) \\
 & Has Child & Has Child LT 5 & Has Child LT 5 & Has Child LT 5 & Has Child LT 5 \\
VARIABLES & All & All & No HS Degree & HS or College & Masters or More \\ \hline
 &  &  &  &  &  \\
\tikzmarkin<2->[hl]{a} Married Women 18-20*& -0.11 & -0.08* & -0.21*** & -0.00 & 0.00 \\
 After*Treatment State & [0.071] & [0.045] & [0.069] & [0.055] & [0.000] \tikzmarkend{a}    \\
 &  &  &  &  &  \\
\tikzmarkin<3->[hl]{b} Married Women 20-25*& -0.07*** & -0.07*** & -0.04 & -0.08*** & -0.38* \\
 After*Treatment State & [0.023] & [0.015] & [0.036] & [0.016] & [0.215] \tikzmarkend{b} \\
 &  &  &  &  &  \\
Married Women 25-30*& -0.00 & 0.03** & 0.19*** & 0.01 & 0.11* \\
After*Treatment State & [0.019] & [0.012] & [0.032] & [0.014] & [0.058] \\
 &  &  &  &  &  \\
Married Women 30-35*& 0.01 & -0.01 & -0.09*** & -0.01 & 0.12** \\
After*Treatment State & [0.020] & [0.012] & [0.029] & [0.014] & [0.051] \\
 &  &  &  &  &  \\
Married Women 35-40*& -0.01 & -0.02** & -0.07*** & -0.03* & 0.10* \\
After*Treatment State & [0.019] & [0.012] & [0.026] & [0.014] & [0.053] \\
 &  &  &  &  &  \\
Observations & 152,366 & 152,366 & 34,081 & 110,324 & 7,961 \\
R-squared & 0.38 & 0.24 & 0.28 & 0.24 & 0.17 \\
 Mean of Dependant Variable & 0.48 & 0.09 & 0.07 & 0.10 & 0.08 \\ \hline \hline
\multicolumn{6}{c}{ Standard errors in brackets} \\
\multicolumn{6}{c}{ *** p$<$0.01, ** p$<$0.05, * p$<$0.1} \\
\end{tabular}
}
\end{center}
\end{frame}

\end{document}