fix: Mapco/Ansum theme: read all button in mobile view (#7873)

Closes #7644

Before:
<img width="212" height="153" alt="grafik" src="https://github.com/user-attachments/assets/628034cf-421a-43c1-a762-21906d99d5d9" />


After:
<img width="249" height="186" alt="grafik" src="https://github.com/user-attachments/assets/8414aa34-4936-44e1-84e4-52dad70477b6" />


How to test the feature manually:

1. use Ansum/Mapco theme
2. have a small screen to see it in the mobile view
3. see the read all button in the normal view

p/themes/Ansum/_mobile.scss

@@ -96,6 +96,10 @@
 		}
 	}
 
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
+
 	#stream {
 		.flux {
 			.flux_header {

p/themes/Ansum/ansum.css

@@ -1275,6 +1275,9 @@ main.prompt {
 	.nav_menu .search .input:focus {
 		width: 400px;
 	}
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
 	#stream .flux .flux_header {
 		padding: 0.5rem 0;
 	}

p/themes/Ansum/ansum.rtl.css

@@ -1275,6 +1275,9 @@ main.prompt {
 	.nav_menu .search .input:focus {
 		width: 400px;
 	}
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
 	#stream .flux .flux_header {
 		padding: 0.5rem 0;
 	}

p/themes/Mapco/_mobile.scss

@@ -103,6 +103,10 @@
 		}
 	}
 
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
+
 	#stream {
 		.flux {
 			.flux_header {

p/themes/Mapco/mapco.css

@@ -1292,6 +1292,9 @@ main.prompt {
 	.nav_menu .search .input:focus {
 		width: 400px;
 	}
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
 	#stream .flux .flux_header {
 		padding: 0.5rem 0;
 	}

p/themes/Mapco/mapco.rtl.css

@@ -1292,6 +1292,9 @@ main.prompt {
 	.nav_menu .search .input:focus {
 		width: 400px;
 	}
+	#nav_menu_read_all #nav_menu_read .dropdown-toggle.btn {
+		background-image: none;
+	}
 	#stream .flux .flux_header {
 		padding: 0.5rem 0;
 	}