GTK3: match titlebutton placement with xfwm4 theme

src/themes/Kali/sass/gtk-sass/_common-tweaks.scss

@@ -177,16 +177,12 @@ headerbar {
 
   &.default-decoration {
     min-height: 0;
-    padding: 3px;
-    border-color: $borders_color;
-
-    &:backdrop { background-color: $base_color; }
+    padding: 6px;
 
     button.titlebutton {
-      min-height: 20px;
-      min-width: 20px;
-      margin: 0 4px;
-      padding: 0;
+      min-height: 0;
+      min-width: 0;
+      margin: 0;
     }
   }
 
@@ -469,8 +465,36 @@ decoration {
 }
 
 // Window Close button
-button.titlebutton {
-  &:not(.appmenu) { margin: 0; }
+button.titlebutton:not(.appmenu) {
+  margin: 0;
+  margin-left: 6px;
+  padding: 0;
+  min-width: 0;
+  min-height: 0;
+  border: 0;
+  -gtk-icon-shadow: none;
+
+  & + & { margin-left: 0; }
+  &:last-child { margin-right: 6px; }
+
+  &:hover {
+    transition: 0;
+    background: transparentize(white, .8);
+    box-shadow: 0 1px 1px $shadow_color, inset 0 0 0 1px $borders_color;
+  }
+
+  @at-root
+  .maximized &,
+  .fullscreen &,
+  .tiled &,
+  .tiled-top &,
+  .tiled-right &,
+  .tiled-bottom &,
+  .tiled-left & {
+      &:last-child { margin-right: 0; }
+      &:first-child { margin-left: 0; }
+  }
+
   &:backdrop {
     background: transparent;
     &:not(:hover) { border-color: transparent; }