You build a dashboard. Sidebar on the left, content on the right, a table or a code block inside. It looks perfect with your sample data. Then a user pastes a long URL into a field, and the whole page grows a horizontal scrollbar. The sidebar gets squeezed, the layout breaks, and you start adding overflow: hidden to everything until the symptoms go away. There is a one-line fix, and it is not overflow: hidden . The Layout That Breaks <div class= "layout" >...