diff --git a/docs/source/_static/.gitkeep b/docs/source/_static/.gitkeep
new file mode 100644
index 0000000..2c13f31
--- /dev/null
+++ b/docs/source/_static/.gitkeep
@@ -0,0 +1 @@
+# Placeholder to ensure the _static directory is tracked for Sphinx builds.
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
index 92edad9..d821672 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -58,6 +58,7 @@ dev = [
     "pytest-mock>=3.15.1",
     # Documentation
     "sphinx==8.1.3",
+    "sphinx-rtd-theme>=3.0.0",
     "sphinx_immaterial>=0.13.8",
     "sphinx-autodoc-typehints==3.0.1",
     "sphinx-copybutton>=0.5.2",
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 2031df6..f9d54b2 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -105,6 +105,8 @@ sphinx==8.1.3
     #   sphinx-autodoc-typehints
     #   sphinx-copybutton
     #   sphinx-immaterial
+sphinx-rtd-theme==3.0.1
+    # via pyUSPTO (pyproject.toml)
 sphinx-autodoc-typehints==3.0.1
     # via pyUSPTO (pyproject.toml)
 sphinx-copybutton==0.5.2