Fix off-by-one error in 'css--hex-to-rgb'

* lisp/textmodes/css-mode.el (css--hex-to-rgb): Fix off-by-one error.

* test/lisp/textmodes/css-mode-tests.el (css-test-hex-to-rgb): Add
regression tests for the above fix.

1 files changed, 1 insertions, 1 deletions

diff --git a/lisp/textmodes/css-mode.el b/lisp/textmodes/css-mode.el
index 6bd08f59190..135c0d5f928 100644
--- a/lisp/textmodes/css-mode.el
+++ b/lisp/textmodes/css-mode.el
@@ -1458,7 +1458,7 @@ should not be mixed with those in color.el."
          (if-let* ((alpha (css--hex-alpha hex))
                    (a (css--format-rgba-alpha
                        (/ (string-to-number alpha 16)
-                          (float (expt 16 (length alpha)))))))
+                          (float (- (expt 16 (length alpha)) 1))))))
              (format "rgba(%d, %d, %d, %s)" r g b a)
            (format "rgb(%d, %d, %d)" r g b))
          t))