diff --git a/.github/workflows/build_docs.yml b/.github/workflows/build_docs.yml
index 7068068e..6a71e1a7 100644
--- a/.github/workflows/build_docs.yml
+++ b/.github/workflows/build_docs.yml
@@ -31,7 +31,7 @@ jobs:
     - name: Install python packages
       run: |
         python -m pip install --upgrade pip
-        pip install sphinx
+        pip install sphinx sphinx-rtd-theme
         cd ${GITHUB_WORKSPACE}/main
         python -m pip install '.[all]'
 
diff --git a/.github/workflows/deploy_docs.yml b/.github/workflows/deploy_docs.yml
index 9e737f42..f19f1f9e 100644
--- a/.github/workflows/deploy_docs.yml
+++ b/.github/workflows/deploy_docs.yml
@@ -37,7 +37,7 @@ jobs:
     - name: Prepare LaTeX env
       run: |
         sudo apt update
-          sudo apt install openmpi-bin libopenmpi-dev
+        sudo apt install openmpi-bin libopenmpi-dev
         sudo apt install \
           texlive-latex-recommended texlive-latex-extra texlive-xetex \
           texlive-lang-japanese texlive-fonts-recommended texlive-fonts-extra latexmk
@@ -46,7 +46,7 @@ jobs:
     - name: Install python packages
       run: |
         python -m pip install --upgrade pip
-        pip install sphinx
+        pip install sphinx sphinx-rtd-theme
 
     - name: Build
       run: |
diff --git a/doc/api/source/conf.py b/doc/api/source/conf.py
index 0fcada98..d8cf36c7 100644
--- a/doc/api/source/conf.py
+++ b/doc/api/source/conf.py
@@ -32,7 +32,7 @@
 # -- Options for HTML output -------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
-html_theme = "haiku"
+html_theme = "sphinx_rtg_theme"
 html_static_path = ['_static']
 
 # -- Options for todo extension ----------------------------------------------