This is expected from the flex rules applied to the other VisualElement in the same container. Since it has flex-grow:1, it will grow to take the available space. Changing the width of the slider to the right will cause the slider on the left to take more space, hence pushing the slider on the right to the right. For more details on flex rules, you can look at this guide to flexbox - https://css-tricks.com/snippets/css/a-guide-to-flexbox/