Using overlay at the top

this is really janky

center-content.el

@@ -2,29 +2,21 @@
 
 ;;; Commentary:
 
-;; This package provides a minor mode `center-content-mode` that centers the visible content
+;; This package provides a minor mode `center-content-mode` that centers the content
-;; of the current buffer both horizontally and vertically. It calculates the necessary margins
+;; of the current buffer both horizontally and vertically. It calculates the necessary
-;; and applies them using overlays and header line adjustments. The mode line is hidden to
+;; margins and applies them using overlays. The mode line is hidden to provide a clean appearance.
-;; provide a clean appearance.
 
 ;;; Code:
 
-(defvar-local center-content--horiz-overlay nil
+(defvar-local center-content--horizontal-overlay nil
-  "Overlay used by `center-content-mode` to add left margin for horizontal centering.")
+  "Overlay used to add left margin for horizontal centering.")
 
-(defvar-local center-content--original-header-line-format nil
+(defvar-local center-content--vertical-overlay nil
-  "Stores the original `header-line-format` to restore upon disabling.")
+  "Overlay used to add top margin for vertical centering.")
 
 (defvar-local center-content--original-mode-line-format nil
   "Stores the original `mode-line-format` to restore upon disabling.")
 
-(defface center-content-header-line
-  `((t (:inherit default
-                 :background ,(face-background 'default nil t)
-                 :foreground ,(face-foreground 'default nil t))))
-  "Face for the header line in `center-content-mode`."
-  :group 'center-content)
-
 (defun center-content--calculate-left-margin ()
   "Calculate the left margin needed to center the content horizontally."
   (let* ((window (selected-window))
@@ -32,15 +24,14 @@
          (content-width (car (window-text-pixel-size
                               window
                               (window-start window)
-                              (window-end window))))
+                              (window-end window)))))
-         (space-width (string-pixel-width " "))
+    (/ (max 0 (- window-width content-width)) 2)))
-         (margin (/ (max 0 (- window-width content-width)) (* 2 space-width))))
-    margin))
 
 (defun center-content--calculate-top-margin ()
   "Calculate the top margin needed to center the content vertically."
-  (let* ((window-height (window-pixel-height))
+  (let* ((window (selected-window))
-         (content-height (cdr (window-text-pixel-size)))
+         (window-height (window-pixel-height window))
+         (content-height (cdr (window-text-pixel-size window)))
          (margin (/ (max 0 (- window-height content-height)) 2)))
     margin))
 
@@ -49,35 +40,38 @@
   (let ((left-margin (center-content--calculate-left-margin))
         (top-margin (center-content--calculate-top-margin)))
     ;; Apply horizontal centering using overlay
-    (let ((horiz-overlay (make-overlay (point-min) (point-max))))
+    (let ((horizontal-overlay (make-overlay (point-min) (point-max))))
-      (overlay-put horiz-overlay 'line-prefix
+      (overlay-put horizontal-overlay 'line-prefix
-                   (propertize " " 'display `(space :width ,left-margin)))
+                   (propertize " " 'display `(space :width (,left-margin))))
-      (setq center-content--horiz-overlay horiz-overlay))
+      (setq center-content--horizontal-overlay horizontal-overlay))
-    ;; Save the original header-line-format
+    ;; Apply vertical centering using a before-string overlay
-    (setq center-content--original-header-line-format header-line-format)
+    (let ((overlay (make-overlay (point-min) (point-min))))
-    ;; Apply vertical centering using header-line-format with custom face
+      (overlay-put overlay 'before-string
-    (setq header-line-format
+                   (propertize "\n" 'display `(space :height (,top-margin))))
-          (propertize " "
+      ;; Set low priority to avoid interfering with line-prefix
-                      'display `(height ,(max 0 (/ top-margin (frame-char-height))))
+      (overlay-put overlay 'priority -50)
-                      'face 'center-content-header-line))
+      (setq center-content--vertical-overlay overlay))
-    ;; Save the original mode-line-format
+    ;; Save and hide the mode line
     (setq center-content--original-mode-line-format mode-line-format)
-    ;; Hide the mode line
+    (setq mode-line-format nil)
-    (setq mode-line-format nil)))
+    ;; Force redisplay
+    (force-mode-line-update)
+    (redisplay)))
 
 (defun center-content--disable ()
   "Disable centering of content."
   ;; Remove horizontal centering overlay
-  (when (overlayp center-content--horiz-overlay)
+  (when (overlayp center-content--horizontal-overlay)
-    (delete-overlay center-content--horiz-overlay)
+    (delete-overlay center-content--horizontal-overlay)
-    (setq center-content--horiz-overlay nil))
+    (setq center-content--horizontal-overlay nil))
-  ;; Restore the original header-line-format
+  ;; Remove vertical centering overlay
-  (setq header-line-format center-content--original-header-line-format)
+  (when (overlayp center-content--vertical-overlay)
-  (setq center-content--original-header-line-format nil)
+    (delete-overlay center-content--vertical-overlay)
+    (setq center-content--vertical-overlay nil))
   ;; Restore the original mode-line-format
   (setq mode-line-format center-content--original-mode-line-format)
   (setq center-content--original-mode-line-format nil)
-  ;; Force redisplay to remove any lingering effects
+  ;; Force redisplay
   (force-mode-line-update)
   (redisplay))
 
@@ -85,7 +79,7 @@
 (define-minor-mode center-content-mode
   "Toggle horizontal and vertical centering of buffer content.
 
-When enabled, the visible content of the buffer is centered both
+When enabled, the content of the buffer is centered both
 horizontally and vertically within the window. The mode line is
 hidden for a clean appearance."
   :init-value nil