Themes: Avoid double hashed value for background-color in custom backgrounds.

This changeset replaces the hardcoded hash symbol with running `maybe_hash_hex_color()` on the full `background-color` value provided via the custom background feature, so the hash is only added if it is needed. By doing so, if a theme developer sets a background color value that uses a hash (#), WordPress won't add an additional hash anymore when outputting the relevant CSS. Duplicate hash symbols (##) can break CSS background color declarations.

Props hovhanneshovakimyan, joyously, poena, 
Fixes #40057.




git-svn-id: https://develop.svn.wordpress.org/trunk@59813 602fd350-edb4-49c9-b593-d223f7449a82

Author: audrasjb

src/wp-admin/includes/class-custom-background.php

@@ -288,7 +288,7 @@ public function admin_page() {
 			$background_styles = '';
 			$bgcolor           = get_background_color();
 			if ( $bgcolor ) {
-				$background_styles .= 'background-color: #' . $bgcolor . ';';
+				$background_styles .= 'background-color: ' . maybe_hash_hex_color( $bgcolor ) . ';';
 			}
 
 			$background_image_thumb = get_background_image();

src/wp-includes/theme.php

@@ -1893,7 +1893,7 @@ function _custom_background_cb() {
 		return;
 	}
 
-	$style = $color ? "background-color: #$color;" : '';
+	$style = $color ? 'background-color: ' . maybe_hash_hex_color( $color ) . ';' : '';
 
 	if ( $background ) {
 		$image = ' background-image: url("' . sanitize_url( $background ) . '");';