This is a collection issue for newer / generally good CSS features to apply to pretalx whenever I find the time:

• Use text-wrap: balance on long-form text; use or text-wrap: pretty on headlines/alerts etc to avoid orphans, which are the most awkward in text that is usually a single line long
• Instead of awkwardly adding margin in HTML or excluding via :last-child, add a CSS class for spaced children (children-mr-1, for example), apply the margin with margin-block-end: , and then use margin-trim: block-end on the parent to just trim off the last margin. Great for button rows.
• Generally, try to use margin-inline-start/end and margin-block-start/end instead of margin-left/right/top/bottom where sensible – especially the inline replacements are great for rtl languages.
• Use CSS layers, especially to unfuck forms css – end up with something like @layer reset, default, themes, patterns, layouts, components, utilities;. Put event css into a layer, too!