\documentclass{article}

\usepackage[a4paper,margin=28mm]{geometry}
\usepackage{osgstyler-lua}
\usepackage{tcolorbox}
\tcbuselibrary{breakable}

% A compact Beamer-like theme. The concrete resources live in osgstyler
% palettes; author commands and environments below only refer to their roles.
\DeclareOsgFontPalette{lecture}{
  main      = {font = {Latin Modern Roman}},
  companion = {font = {Latin Modern Sans}},
  display   = {alias = companion},
  accent    = {alias = companion},
  mono      = {font = {Latin Modern Mono}},
  symbol    = {alias = main}
}

\DeclareOsgColorPalette{lecture}{
  primary    = {model=RGB, value={42,78,121}},
  secondary  = {model=RGB, value={92,112,132}},
  accent     = {model=RGB, value={42,78,121}},
  text       = {model=RGB, value={28,32,36}},
  background = {model=RGB, value={255,255,255}},
  structure  = {alias=primary},
  alert      = {model=RGB, value={178,45,45}},
  example    = {model=RGB, value={43,125,79}}
}

\DeclareOsgMetricPalette{lecture}{
  spacing = {sm = {.5\baselineskip}, md = {.9\baselineskip}},
  padding = {compact = {.35em}, normal = {.65em}},
  rule    = {thin = {.45pt}, normal = {.8pt}},
  radius  = {small = {2pt}}
}

\UseOsgFontPalette{lecture}
\UseOsgColorPalette{lecture}
\UseOsgMetricPalette{lecture}

% Beamer-like inline roles. Both spellings are provided deliberately:
% \structure is Beamer's command, while \struct is a convenient short form.
\DeclareOsgInlineStyle{alert-text}{
  font = none, weight = bold, shape = inherit,
  color = alert, decoration = none, semantics = strong
}
\DeclareOsgInlineStyle{structure-text}{
  font = none, weight = bold, shape = inherit,
  color = structure, decoration = none, semantics = none
}
\BindOsgInlineCommand{\alert}{alert-text}
\BindOsgInlineCommand{\structure}{structure-text}
\BindOsgInlineCommand{\struct}{structure-text}

% tcolorbox is only the renderer. Colors, typography, rules, radii, padding,
% and spacing are resolved through the active osgstyler palettes.
\tcbset{
  osg beamer block/.style={
    breakable,
    colback=\OsgColorName{background},
    coltext=\OsgColorName{text},
    boxrule=\OsgMetric{rule}{normal},
    arc=\OsgMetric{radius}{small},
    left=\OsgMetric{padding}{normal},
    right=\OsgMetric{padding}{normal},
    top=\OsgMetric{padding}{compact},
    bottom=\OsgMetric{padding}{compact},
    before skip=\OsgMetric{spacing}{md},
    after skip=\OsgMetric{spacing}{md},
    fonttitle=\UseOsgFont{accent}\bfseries,
    coltitle=\OsgColorName{background}
  }
}

\newtcolorbox{block}[1]{
  osg beamer block,
  title={#1},
  colframe=\OsgColorName{structure},
  colbacktitle=\OsgColorName{structure}
}
\newtcolorbox{alertblock}[1]{
  osg beamer block,
  title={#1},
  colframe=\OsgColorName{alert},
  colbacktitle=\OsgColorName{alert}
}
\newtcolorbox{exampleblock}[1]{
  osg beamer block,
  title={#1},
  colframe=\OsgColorName{example},
  colbacktitle=\OsgColorName{example}
}

\title{Beamer-like formatting with \texttt{osgstyler}}
\author{osglecture example}
\date{}

\begin{document}
\maketitle

\section{Inline roles}

The commands \structure{structure the exposition}, \struct{use the same
role through a short alias}, and \alert{draw attention to an important
statement}. Their appearance can be changed without redefining the commands.

\section{Block roles}

\begin{block}{Ordinary block}
  This corresponds to Beamer's neutral \texttt{block}. Its visual structure
  uses the palette's \structure{structure colour}.
\end{block}

\begin{alertblock}{Alert block}
  This material requires attention. Inline \alert{alert text} and the block
  share a color role, but retain distinct inline and block semantics.
\end{alertblock}

\begin{exampleblock}{Example block}
  Examples receive their own palette slot and can therefore remain visually
  distinct when the complete theme is exchanged.
\end{exampleblock}

\end{document}