Réseau de neurones (3 couches) en TikZ — input, hidden, output

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning, calc}

\begin{document}
\begin{tikzpicture}[
  >=stealth,
  every neuron/.style={
    circle, draw, thick, minimum size=22pt, inner sep=0pt
  },
  input/.style ={every neuron, fill=blue!15, draw=blue!60!black},
  hidden/.style={every neuron, fill=green!15, draw=green!60!black},
  output/.style={every neuron, fill=red!15, draw=red!60!black},
  every label/.style={font=\footnotesize\bfseries}
]

  % --- Input layer (3 neurons) ---
  \foreach \i [count=\y from 0] in {1,2,3}
    \node[input] (I-\i) at (0, -\y * 1.2) {$x_{\i}$};

  % --- Hidden layer (4 neurons) ---
  \foreach \i [count=\y from 0] in {1,2,3,4}
    \node[hidden] (H-\i) at (3, -\y * 1.2 + 0.6) {$h_{\i}$};

  % --- Output layer (2 neurons) ---
  \foreach \i [count=\y from 0] in {1,2}
    \node[output] (O-\i) at (6, -\y * 1.2 - 0.6) {$y_{\i}$};

  % --- Fully connected edges ---
  \foreach \i in {1,2,3}
    \foreach \j in {1,2,3,4}
      \draw[gray!60, thin] (I-\i) -- (H-\j);

  \foreach \i in {1,2,3,4}
    \foreach \j in {1,2}
      \draw[gray!60, thin] (H-\i) -- (O-\j);

  % --- Layer labels ---
  \node[above=12pt of I-1, blue!60!black]   {\textbf{Input}};
  \node[above=12pt of H-1, green!60!black]  {\textbf{Hidden}};
  \node[above=12pt of O-1, red!60!black]    {\textbf{Output}};

\end{tikzpicture}
\end{document}