How to “fix baselines” in tikz nodes?

Question

I want to define nodes which are shapes with some text in it using \ce{} from the mhchem package. How would I go around ensuring the baselines are the same between nodes, right now it shifts if I use subscript. Here's a MWE:

\documentclass{article}
\usepackage[version=3]{mhchem}

\usepackage{tikz}
\usetikzlibrary{shapes}

\newbox\nodebox
\newcommand\mycommand[2]{%
    \begin{tikzpicture}%
        \node[text=#1, rectangle, inner ysep=4pt, inner xsep=2pt, rounded corners=7, minimum height=5mm, minimum width=10mm, fill=#1] {\tiny\sffamily \textbf{\ce{#2}}};
        \node[yshift=-0.5,text=black!95!white] {\scriptsize\sffamily \textbf{\ce{#2}}};
        \node[text=white] {\scriptsize\sffamily \textbf{\ce{#2}}};
    \end{tikzpicture}%
}

\begin{document}

\mycommand{red!40!white}{Al2O3} \mycommand{blue!40!white}{Al}

\end{document}

Answer 1

In this case, you need to manually set the text depth of all nodes to the same value. If you set it to text depth=0pt, the text will be aligned as if there were no descenders or subscripts, if you set it to something like text depth=0.25ex, the text in all nodes will be aligned as if there were.

\documentclass{article}
\usepackage[version=3]{mhchem}

\usepackage{tikz}
\usetikzlibrary{shapes}

\newbox\nodebox
\newcommand\mycommand[2]{%
    \begin{tikzpicture}[every node/.append style={text depth=0.25ex}]%
        \node[
            text=#1,
            rectangle,
            inner ysep=4pt,
            inner xsep=2pt,
            rounded corners=7,
            minimum height=5mm,
            minimum width=10mm,
            fill=#1
        ] {\tiny\sffamily \textbf{\ce{#2}}};
        \node[
            yshift=-0.5,
            text=black!95!white
        ] {\scriptsize\sffamily \textbf{\ce{#2}}};
        \node[text=white]{\scriptsize\sffamily\textbf{\ce{#2}}};
    \end{tikzpicture}%
}

\begin{document}

\mycommand{red!40!white}{Al2O3} \mycommand{blue!40!white}{Al}

\end{document}