nitro theme: tuck adjacent buttons under the right slant

A -0.8em right margin pulls whatever follows an article button (another
button or text) under the slant's empty top triangle: adjacent buttons'
slant bands overlap horizontally by ~0.3em while the painted parallel
edges keep a constant ~0.3em clearance — overlapping but never touching.

pagerite/themes/nitro/theme.css

@@ -151,7 +151,12 @@
    subordinate). border-radius is the fallback for browsers without
    shape(). Asymmetric inline padding keeps the text clear of the
    slants (wider on the right: the wide bottom-right sweep cuts deeper
-   into the label's end side). Editor chrome (.icon-btn pens, .copy)
+   into the label's end side). The negative right margin tucks whatever
+   follows — another button or plain text — under the right slant's
+   empty top triangle: adjacent buttons' slant bands overlap by ~0.3em
+   horizontally while the painted edges keep ~0.3em apart (the slants
+   are parallel, so the clearance is constant top to bottom).
+   Editor chrome (.icon-btn pens, .copy)
    keeps its own styling. The {contact:} envelope's line-height is
    reduced in the base stylesheet so it doesn't outgrow this height. */
 .contact-trigger,
@@ -161,6 +166,7 @@ article button:not(.icon-btn):not(.copy) {
   justify-content: center;
   height: 1.7em;
   padding: 0 1.3em 0 1em;
+  margin-right: -0.8em;
   white-space: nowrap;
   /* Same typography as the contact trigger (raw <button>s otherwise get
      the small UA font): nav family/weight, article size and leading. */