Merge branch '5.3' into 5.4

diff --cc wcfsetup/install/files/style/layout/pageHeader.scss
index 068f183608c84562695f920177e394835f5a617b,e5dbfa609bb7db88b5a41f961369b15d2aaf717f..8bbfc33c6653e254ec175b1a63f1a2badcc3cacd
--- 1/wcfsetup/install/files/style/layout/pageHeader.scss
--- 2/wcfsetup/install/files/style/layout/pageHeader.scss
+++ b/wcfsetup/install/files/style/layout/pageHeader.scss
@@@ -204,14 -208,14 +204,14 @@@
                        visibility: visible;
                }
        }
 -      
 +
        .mainMenuShowPrevious {
-               background: linear-gradient(to left, transparent 0%, $wcfHeaderMenuBackground 75%);
+               background: linear-gradient(to left, transparentize($wcfHeaderMenuBackground, 1) 0%, $wcfHeaderMenuBackground 75%);
                left: 0;
        }
 -      
 +
        .mainMenuShowNext {
-               background: linear-gradient(to right, transparent 0%, $wcfHeaderMenuBackground 75%);
+               background: linear-gradient(to right, transparentize($wcfHeaderMenuBackground, 1) 0%, $wcfHeaderMenuBackground 75%);
                justify-content: flex-end;
                right: 0;
        }