Cherry-pick 278418@main (0995cf2). https://bugs.webkit.org/show_bug.c…

…gi?id=255585

    [GTK] Extraneous empty bar shown in detached inspector windows
    https://bugs.webkit.org/show_bug.cgi?id=255585

    Reviewed by Carlos Garcia Campos.

    The WI.undockedTitleAreaHeight() function only returns non-zero values
    for Mac, but in Variables.css the --undocked-title-area-height variable
    is set always to a non-zero value, the exact value depending on the
    MacOS version. Add an :is(.mac-platform) match to leave the value
    unchanged from zero in any non-Mac platform to keep the value in sync
    with what WI.undockedTitleAreaHeight() returns.

    * Source/WebInspectorUI/UserInterface/Views/Variables.css: Only change
      the --undocked-title-area-height variable for Mac.

    Canonical link: https://commits.webkit.org/278418@main

Canonical link: https://commits.webkit.org/274313.205@webkitglib/2.44

Source/WebInspectorUI/UserInterface/Views/Variables.css

@@ -261,7 +261,7 @@ body:is(.mac-platform.monterey, .mac-platform.big-sur) {
     --sorted-header-font-weight: 700;
 }
 
-body:not(.mac-platform.monterey, .mac-platform.big-sur):not(.docked) {
+body:is(.mac-platform):not(.mac-platform.monterey, .mac-platform.big-sur):not(.docked) {
     /* keep in sync with `WI.undockedTitleAreaHeight` */
     --undocked-title-area-height: calc(22px / var(--zoom-factor));
 }