fix: lock page scroll when Dialog is open

thaw/src/dialog/dialog.rs

@@ -2,7 +2,7 @@ use crate::ConfigInjection;
 use leptos::{context::Provider, ev, prelude::*};
 use thaw_components::{FocusTrap, Teleport};
 use leptos_transition_group::CSSTransition;
-use thaw_utils::{class_list, mount_style, Model};
+use thaw_utils::{class_list, mount_style, use_lock_html_scroll, Model};
 
 #[component]
 pub fn Dialog(
@@ -21,6 +21,11 @@ pub fn Dialog(
     mount_style("dialog", include_str!("./dialog.css"));
     let config_provider = ConfigInjection::expect_context();
 
+    // Prevent the page behind the backdrop from scrolling while the dialog
+    // is open. Same as OverlayDrawer — the Dialog was the only overlay
+    // component missing this.
+    use_lock_html_scroll(open.signal());
+
     let on_mask_click = move |_| {
         if mask_closeable.get_untracked() {
             open.set(false);

thaw_utils/src/hooks/use_lock_html_scroll.rs

@@ -24,8 +24,8 @@ pub fn use_lock_html_scroll(is_lock: Signal<bool>) {
                 let style = document()
                     .create_element("style")
                     .expect("create style element error");
-                _ = style.set_attribute("data-id", &format!("thaw-lock-html-scroll"));
-                style.set_text_content(Some("html { overflow: hidden; }"));
+                _ = style.set_attribute("data-id", "thaw-lock-html-scroll");
+                style.set_text_content(Some(&lock_scroll_css()));
                 _ = head.append_child(&style);
                 style_el.update_value(move |el| {
                     *el = SendWrapper::new(Some(style));
@@ -48,3 +48,31 @@ pub fn use_lock_html_scroll(is_lock: Signal<bool>) {
         _ = is_lock;
     }
 }
+
+/// Build the CSS rule that locks scrolling and compensates for the scrollbar.
+///
+/// When `overflow: hidden` removes the scrollbar, the viewport widens by
+/// the scrollbar's width, causing `margin: auto` centered content to shift.
+/// Adding `padding-right` equal to the scrollbar width keeps the layout stable.
+#[cfg(any(feature = "csr", feature = "hydrate"))]
+fn lock_scroll_css() -> String {
+    use leptos::prelude::document;
+
+    let scrollbar_width = document()
+        .document_element()
+        .map(|html| {
+            let client_w = html.client_width();
+            let window_w = web_sys::window()
+                .and_then(|w| w.inner_width().ok())
+                .and_then(|v| v.as_f64())
+                .unwrap_or(0.0) as i32;
+            window_w - client_w
+        })
+        .unwrap_or(0);
+
+    if scrollbar_width > 0 {
+        format!("html {{ overflow: hidden; padding-right: {scrollbar_width}px; }}")
+    } else {
+        "html { overflow: hidden; }".to_string()
+    }
+}