appview: prevent content shift when content overflows

in profile pages, when expanding activities, it can cause a page to
begin overflowing. this settings reserves space for the scrollbar
upfront.

Signed-off-by: oppiliappan <[e-mail]>

input.css

···
     @layer base {
         html {
             font-size: 14px;
+            scrollbar-gutter: stable;
         }
         @supports (font-variation-settings: normal) {
             html {