Bookmarklet to hide everything but the channel on a Slack page.

slackKiosk.js

javascript:(function(){
s = ".p-workspace__primary_view";
function x(attr, val){document.querySelector(s).style[attr]=val;}
x('position', 'fixed');
x('background-color', 'white');
x('top', 0);
x('right', 0);
x('left', 0);
x('bottom', 0);
})();