The responsiveness feature can be applied in a few ways, starting with the page itself, and several settings come into play, but not all at the same time. It’s quite the rabbit hole, so let’s get tumbling…
When ‘fixed width’ is unchecked (which your single floating group header should always be), you can set the ‘minimum width’ (which is in %). You can also then enable ‘maximum width’ (also in %, but leave unchecked for floating headers as they usually span the whole width anyway).
You may want to create a reusable group of your header, insert a blank floating group in each page that needs it, and insert the reusable header group into the floating group:
Now you can add your logo inside, set it to ‘left’ and ‘fixed width’ (also, more below). Now insert the login button (actually never do exactly this, see below) on the right side, and set it’s alignment to ‘right’. Here you have a choice of keeping it fixed width or not. If in doubt, test with it unchecked and use the responsive page slider at the top to shrink/widens the page and see what happens. I have yet to see anything different happen in ‘live’ version versus testing it here. When I don’t get what I expect, it always ends up being a matter of tweaking a setting (fixed width, minimum width, and max width), or two elements overlapping (also, more below).
For a useful ‘fixed width’ application insert a group (of fixed width) inside the floating group (which is not fixed width and no max width), right-aligned, and touching the right edge. Inside the group insert one or two buttons, or anything your want, with fixed width (login button, signup button, for example). Leave space between the right-most object inside the group, and the right edge of the group. The width of this gap will now not change as the page width changes. When the page widens, the floating group widens as well, but the group inside sticks to right edge while keeping the same width, including the button(s) inside. And the button will remain in place inside the group.
This is because the group inserted inside the floating group is touching the right edge. If there is a gap between the group and the right edge of the floating group, that gap gets bigger as the page widens (looks terrible). This will also happen to buttons placed directly inside a floating group. As the floating group widens, the gap between the button and right-edge of the page will increase. Inserting a fixed-width group is a good trick to keep one or several things together without changing their size, while keeping them aligned to the sides of responsive pages.
Also, I find it better to build a page at its minimum width and tweak it as it widens, rather than building a wide page and trying to keep elements ligned up vertically when the page shrinks. This is because you can build the elements on a narrow page already ligned up, and then adjust their maximum widths and decide if/when elements should get bumped up to be beside each other as the page widens, of you’re using that feature (‘Wrap to previous line if the page is stretched’).
For your logo, you can use the feature that collapses/hides it (‘Add Hiding Rule’) if the page becomes small enough, which you predefine. If triggered, the logo’s visibility will be set to ‘no’. You can use this as a condition for another smaller logo that is initially hidden, but becomes visible if your main logo isn’t visible.
Also, be very careful about any elements overlapping, or sometimes even touching. The responsiveness engine doesn’t just dislike it, but hates it. You’ll get all kinds of frustrating errors which happen after you’ve done everything else correctly. When the responsive engine appears to have ‘broken’, two elements are probably overlapping or touching. This could be an input field and a text above it with the input’s name, for example. Make the adjustments then test with the page width slider.
This might be alot to digest without pictures, or even confusing. Hope this helps.