diff --git a/src/html/classes.rs b/src/html/classes.rs
index 2fd2fbf4..0123d383 100644
--- a/src/html/classes.rs
+++ b/src/html/classes.rs
@@ -3,33 +3,44 @@ use crate::{builder_fn, AutoDefault};
 use std::borrow::Cow;
 
 /// Operaciones disponibles sobre la lista de clases en [`Classes`].
+///
+/// Cada variante opera sobre **una o más clases** proporcionadas como una cadena separada por
+/// espacios (p. ej. `"btn active"`), que se normalizan internamente a minúsculas en
+/// [`Classes::with_classes()`].
 pub enum ClassesOp {
-    /// Añade al final (si no existe).
+    /// Añade las clases que no existan al final.
     Add,
-    /// Añade al principio.
+    /// Añade las clases que no existan al principio.
     Prepend,
-    /// Elimina la(s) clase(s) indicada(s).
+    /// Elimina las clases indicadas que existan.
     Remove,
-    /// Sustituye una o varias clases por otras nuevas (`Replace("old other".into())`).
+    /// Sustituye una o varias clases existentes (indicadas en la variante) por las clases
+    /// proporcionadas.
     Replace(Cow<'static, str>),
     /// Alterna presencia/ausencia de una o más clases.
+    ///
+    /// Si en una misma llamada se repite una clase (p. ej. `"a a"`) que ya existe, el resultado
+    /// mantiene la pertenencia pero puede cambiar el orden (primero se elimina y luego se añade al
+    /// final).
     Toggle,
-    /// Sustituye toda la lista.
+    /// Sustituye la lista completa por las clases indicadas.
     Set,
 }
 
-/// Cadena de clases CSS normalizadas para el atributo `class` de HTML.
+/// Lista de clases CSS normalizadas para el atributo `class` de HTML.
 ///
 /// Permite construir y modificar dinámicamente con [`ClassesOp`] una lista de clases CSS
 /// normalizadas.
 ///
 /// # Normalización
 ///
-/// - El [orden de las clases no es relevante](https://stackoverflow.com/a/1321712) en CSS, pero
-///   [`ClassesOp`] ofrece operaciones para controlar su orden de aparición.
-/// - Las clases se convierten a minúsculas.
-/// - No se permiten clases duplicadas.
+/// - Aunque el orden de las clases en el atributo `class` no afecta al resultado en CSS,
+///   [`ClassesOp`] ofrece operaciones para controlar su orden de aparición por legibilidad.
+/// - Las clases se almacenan en minúsculas.
+/// - No se permiten clases duplicadas tras la normalización (por ejemplo, `Btn` y `btn` se
+///   consideran la misma clase).
 /// - Las clases vacías se ignoran.
+/// - Sin clases, [`get()`](Self::get) devuelve `None` (no `Some("")`).
 ///
 /// # Ejemplo
 ///
@@ -59,53 +70,62 @@ impl Classes {
     /// lista de clases actual.
     #[builder_fn]
     pub fn with_classes(mut self, op: ClassesOp, classes: impl AsRef<str>) -> Self {
-        let classes = classes.as_ref().to_ascii_lowercase();
-        let classes: Vec<&str> = classes.split_ascii_whitespace().collect();
-
-        if classes.is_empty() {
-            return self;
-        }
-
+        let classes = classes.as_ref();
         match op {
             ClassesOp::Add => {
-                self.add(&classes, self.0.len());
+                self.add(classes, self.0.len());
             }
             ClassesOp::Prepend => {
-                self.add(&classes, 0);
+                self.add(classes, 0);
             }
             ClassesOp::Remove => {
-                for class in classes {
-                    self.0.retain(|c| c != class);
+                let mut classes_to_remove = classes.split_ascii_whitespace();
+
+                // 0 clases: no se hace nada.
+                let Some(first) = classes_to_remove.next() else {
+                    return self;
+                };
+
+                // 1 clase: un único *retain*, cero reservas extra.
+                let first = first.to_ascii_lowercase();
+                let Some(second) = classes_to_remove.next() else {
+                    self.0.retain(|c| c != &first);
+                    return self;
+                };
+
+                // 2+ clases: se construye lista para borrar y un único *retain*.
+                let mut to_remove = Vec::new();
+                to_remove.push(first);
+                to_remove.push(second.to_ascii_lowercase());
+                for class in classes_to_remove {
+                    to_remove.push(class.to_ascii_lowercase());
                 }
+                self.0.retain(|c| !to_remove.iter().any(|r| r == c));
             }
             ClassesOp::Replace(classes_to_replace) => {
                 let mut pos = self.0.len();
-                let replace = classes_to_replace.to_ascii_lowercase();
-                let replace: Vec<&str> = replace.split_ascii_whitespace().collect();
-                for class in replace {
-                    if let Some(replace_pos) = self.0.iter().position(|c| c == class) {
+                for class in classes_to_replace.split_ascii_whitespace() {
+                    let class = class.to_ascii_lowercase();
+                    if let Some(replace_pos) = self.0.iter().position(|c| c == &class) {
                         self.0.remove(replace_pos);
-                        if pos > replace_pos {
-                            pos = replace_pos;
-                        }
+                        pos = pos.min(replace_pos);
                     }
                 }
-                self.add(&classes, pos);
+                self.add(classes, pos);
             }
             ClassesOp::Toggle => {
-                for class in classes {
-                    if !class.is_empty() {
-                        if let Some(pos) = self.0.iter().position(|c| c.eq(class)) {
-                            self.0.remove(pos);
-                        } else {
-                            self.0.push(class.to_string());
-                        }
+                for class in classes.split_ascii_whitespace() {
+                    let class = class.to_ascii_lowercase();
+                    if let Some(pos) = self.0.iter().position(|c| c == &class) {
+                        self.0.remove(pos);
+                    } else {
+                        self.0.push(class);
                     }
                 }
             }
             ClassesOp::Set => {
                 self.0.clear();
-                self.add(&classes, 0);
+                self.add(classes, 0);
             }
         }
 
@@ -113,10 +133,16 @@ impl Classes {
     }
 
     #[inline]
-    fn add(&mut self, classes: &[&str], mut pos: usize) {
-        for &class in classes {
-            if !class.is_empty() && !self.0.iter().any(|c| c == class) {
-                self.0.insert(pos, class.to_string());
+    fn add(&mut self, classes: &str, mut pos: usize) {
+        for class in classes.split_ascii_whitespace() {
+            let class = class.to_ascii_lowercase();
+            // Inserción segura descartando duplicados.
+            if !self.0.iter().any(|c| c == &class) {
+                if pos >= self.0.len() {
+                    self.0.push(class);
+                } else {
+                    self.0.insert(pos, class);
+                }
                 pos += 1;
             }
         }
@@ -133,9 +159,32 @@ impl Classes {
         }
     }
 
-    /// Devuelve `true` si la clase está presente.
+    /// Devuelve `true` si **una única clase** está presente.
+    ///
+    /// Si necesitas comprobar varias clases, usa [`contains_all()`](Self::contains_all) o
+    /// [`contains_any()`](Self::contains_any).
     pub fn contains(&self, class: impl AsRef<str>) -> bool {
-        let class = class.as_ref().to_ascii_lowercase();
-        self.0.iter().any(|c| c == &class)
+        self.contains_class(class.as_ref())
+    }
+
+    /// Devuelve `true` si **todas** las clases indicadas están presentes.
+    pub fn contains_all(&self, classes: impl AsRef<str>) -> bool {
+        classes
+            .as_ref()
+            .split_ascii_whitespace()
+            .all(|class| self.contains_class(class))
+    }
+
+    /// Devuelve `true` si **alguna** de las clases indicadas está presente.
+    pub fn contains_any(&self, classes: impl AsRef<str>) -> bool {
+        classes
+            .as_ref()
+            .split_ascii_whitespace()
+            .any(|class| self.contains_class(class))
+    }
+
+    #[inline]
+    fn contains_class(&self, class: &str) -> bool {
+        self.0.iter().any(|c| c.eq_ignore_ascii_case(class))
     }
 }
diff --git a/tests/html_classes.rs b/tests/html_classes.rs
new file mode 100644
index 00000000..00de96c5
--- /dev/null
+++ b/tests/html_classes.rs
@@ -0,0 +1,199 @@
+use pagetop::prelude::*;
+
+fn assert_classes(c: &Classes, expected: Option<&str>) {
+    let got = c.get();
+    assert_eq!(got.as_deref(), expected, "Expected {:?}, got {:?}", expected, got);
+}
+
+// **< Construction & invariants (new/get) >********************************************************
+
+#[pagetop::test]
+async fn classes_new_empty_and_whitespace_is_empty() {
+    assert_classes(&Classes::new(""), None);
+    assert_classes(&Classes::new("   "), None);
+    assert_classes(&Classes::new("\t\n\r  "), None);
+}
+
+#[pagetop::test]
+async fn classes_new_normalizes_and_dedups_and_preserves_first_occurrence_order() {
+    let c = Classes::new("Btn btn BTN  btn-primary  BTN-PRIMARY");
+    assert_classes(&c, Some("btn btn-primary"));
+    assert!(c.contains("BTN"));
+    assert!(c.contains("btn-primary"));
+}
+
+#[pagetop::test]
+async fn classes_get_returns_none_when_empty_some_when_not() {
+    assert_classes(&Classes::new(" "), None);
+    assert_classes(&Classes::new("a"), Some("a"));
+}
+
+// **< Basic operations (add/prepend/set) >*********************************************************
+
+#[pagetop::test]
+async fn classes_add_appends_unique_and_normalizes() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Add, "C b  D");
+    assert_classes(&c, Some("a b c d"));
+}
+
+#[pagetop::test]
+async fn classes_add_ignores_empty_input() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Add, "   \t");
+    assert_classes(&c, Some("a b"));
+}
+
+#[pagetop::test]
+async fn classes_add_same_tokens() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Add, "A B a b");
+    assert_classes(&c, Some("a b"));
+}
+
+#[pagetop::test]
+async fn classes_prepend_inserts_at_front_preserving_new_order() {
+    let c = Classes::new("c d").with_classes(ClassesOp::Prepend, "A b");
+    assert_classes(&c, Some("a b c d"));
+}
+
+#[pagetop::test]
+async fn classes_prepend_inserts_new_tokens_skipping_duplicates() {
+    let c = Classes::new("b c").with_classes(ClassesOp::Prepend, "a b d");
+    assert_classes(&c, Some("a d b c"));
+}
+
+#[pagetop::test]
+async fn classes_prepend_ignores_empty_input() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Prepend, "");
+    assert_classes(&c, Some("a b"));
+}
+
+#[pagetop::test]
+async fn classes_set_replaces_entire_list_and_dedups() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Set, "X  y  y  Z");
+    assert_classes(&c, Some("x y z"));
+}
+
+#[pagetop::test]
+async fn classes_set_with_empty_input_clears() {
+    let base = Classes::new("a b");
+    let c = base.with_classes(ClassesOp::Set, " \n ");
+    assert_classes(&c, None);
+}
+
+// **< Mutation operations (remove/toggle/replace) >************************************************
+
+#[pagetop::test]
+async fn classes_remove_is_case_insensitive() {
+    let c = Classes::new("a b c d").with_classes(ClassesOp::Remove, "B  D");
+    assert_classes(&c, Some("a c"));
+}
+
+#[pagetop::test]
+async fn classes_remove_non_existing_is_noop() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Remove, "x y z");
+    assert_classes(&c, Some("a b c"));
+}
+
+#[pagetop::test]
+async fn classes_remove_with_extra_whitespace() {
+    let c = Classes::new("a b c d").with_classes(ClassesOp::Remove, "   b\t\t  \n d  ");
+    assert_classes(&c, Some("a c"));
+}
+
+#[pagetop::test]
+async fn classes_toggle_removes_if_present_case_insensitive() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Toggle, "B");
+    assert_classes(&c, Some("a c"));
+}
+
+#[pagetop::test]
+async fn classes_toggle_adds_if_missing_and_normalizes() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Toggle, "C");
+    assert_classes(&c, Some("a b c"));
+}
+
+#[pagetop::test]
+async fn classes_toggle_multiple_tokens_is_sequential_and_order_dependent() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Toggle, "C  B   A");
+    assert_classes(&c, Some("c"));
+}
+
+#[pagetop::test]
+async fn classes_toggle_duplicate_tokens_are_applied_sequentially() {
+    let c = Classes::new("b").with_classes(ClassesOp::Toggle, "a a");
+    assert_classes(&c, Some("b"));
+
+    let c = Classes::new("a b").with_classes(ClassesOp::Toggle, "a a");
+    assert_classes(&c, Some("b a"));
+}
+
+#[pagetop::test]
+async fn classes_replace_removes_targets_and_inserts_new_at_min_position() {
+    let c = Classes::new("a b c d").with_classes(ClassesOp::Replace("c a".into()), "x y");
+    assert_classes(&c, Some("x y b d"));
+}
+
+#[pagetop::test]
+async fn classes_replace_when_none_found_appends_at_end() {
+    let c = Classes::new("a b").with_classes(ClassesOp::Replace("x y".into()), "c d");
+    assert_classes(&c, Some("a b c d"));
+}
+
+#[pagetop::test]
+async fn classes_replace_is_case_insensitive_on_targets_and_new_values_are_normalized() {
+    let c = Classes::new("btn btn-primary active")
+        .with_classes(ClassesOp::Replace("BTN-PRIMARY".into()), "Btn-Secondary");
+    assert_classes(&c, Some("btn btn-secondary active"));
+}
+
+#[pagetop::test]
+async fn classes_replace_with_empty_new_removes_only() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Replace("b".into()), "   ");
+    assert_classes(&c, Some("a c"));
+}
+
+#[pagetop::test]
+async fn classes_replace_dedups_against_existing_items() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Replace("b".into()), "c d");
+    assert_classes(&c, Some("a d c"));
+}
+
+#[pagetop::test]
+async fn classes_replace_ignores_target_whitespace_and_repetition() {
+    let c = Classes::new("a b c").with_classes(ClassesOp::Replace("  b  b ".into()), "x y");
+    assert_classes(&c, Some("a x y c"));
+}
+
+// **< Queries (contains) >*************************************************************************
+
+#[pagetop::test]
+async fn classes_contains_single() {
+    let c = Classes::new("btn btn-primary");
+    assert!(c.contains("btn"));
+    assert!(c.contains("BTN"));
+    assert!(!c.contains("missing"));
+}
+
+#[pagetop::test]
+async fn classes_contains_all_and_any() {
+    let c = Classes::new("btn btn-primary active");
+
+    assert!(c.contains_all("btn active"));
+    assert!(c.contains_all("BTN BTN-PRIMARY"));
+    assert!(!c.contains_all("btn missing"));
+
+    assert!(c.contains_any("missing active"));
+    assert!(c.contains_any("BTN-PRIMARY missing"));
+    assert!(!c.contains_any("missing other"));
+}
+
+// **< Properties / regression (combined sequences, ordering) >*************************************
+
+#[pagetop::test]
+async fn classes_order_is_stable_for_existing_items() {
+    let c = Classes::new("a b c")
+        .with_classes(ClassesOp::Add, "d") // a b c d
+        .with_classes(ClassesOp::Prepend, "x") // x a b c d
+        .with_classes(ClassesOp::Remove, "b") // x a c d
+        .with_classes(ClassesOp::Add, "b"); // x a c d b
+    assert_classes(&c, Some("x a c d b"));
+}