diff --git a/lang/cs.css b/lang/cs.css
new file mode 100644
index 0000000..b6b5153
--- /dev/null
+++ b/lang/cs.css
@@ -0,0 +1,4 @@
+:lang(cs) .theorem::before { content: 'Teorém ' counter(theorem) '. ' !important; }
+:lang(cs) .lemma::before { content: 'Lemma ' counter(theorem) '. ' !important; }
+:lang(cs) .proof::before { content: 'Důkaz. ' attr(title) !important; }
+:lang(cs) .definition::before { content: 'Definice ' counter(definition) '. ' !important; }
diff --git a/languages.html b/languages.html
index 06d6c86..85f0e51 100644
--- a/languages.html
+++ b/languages.html
@@ -39,6 +39,7 @@
     <select name="language" id="language-select">
       <option value="en">English (en)</option>
       <!-- ↓ Sort alphabetically ↓ -->
+      <option value="cs">Czech (cs)</option>
       <option value="de">German (de)</option>
       <option value="dk">Danish (dk)</option>
       <option value="es">Spanish (es)</option>