The Fullscreen Slider is set to 100% width&height but shows a blank ∼5px border on the left&right depending on the viewport size. Upon browser resize, it scales to full width. (tested on Chrome and Safari)
From the main page of the desktop version (https://lady-helen.com), „Images“ opens a page based on the Fullscreen Slider. The blank border gets visible, when the viewport size is around 1050x740px. (landscape images only)
Many thanks for your help!