[MM-51881]: btn-primary SCSS leaves button white when not focussed (#23209)

webapp/channels/src/sass/layout/_webhooks.scss

@@ -376,7 +376,6 @@
                 border-width: 1px;
                 border-style: solid;
                 margin: 8px 8px 0 0;
-                background: var(--center-channel-bg);
                 border-radius: 3px;
                 font-size: 13px;
                 font-weight: 700;