No margin / padding on mobile screens

Hallo,

I just startet to set up a new website. It’s still a very basic WP-install – just some test pages) with Sydney theme + Child theme. I included the full width row-code of this thread to enable elements marked as “alignfull” to stretch to the full width of the browser window (not just the content area). This works fine.

Problem: Headers and text look good on larger screens and tablets, but don’t have any padding / margin on smartphones (going from edge to edge of the display, making it hard to read).

I tried to add CSS like .entry-content { padding-left: 15px; padding-right: 15px;}. But this also applies to fullwidth-elements. If I add .alignfull { margin-left: -15px; margin-right: -15px;} :-/

Can someone help me to find the correct CSS?

Many thanks in advance!
Oliver

The page I need help with: [log in to see the link]