Hi there Daniela!
Great question! While Unbounce pages are Mobile Responsive, Unbounce page layouts aren’t fluid, which means that it’s not possible to create pages on mobile based on percentage widths. While fluid layouts are based on proportionally laying out your website so elements take up the same percent of space on different screen sizes, Responsive Design uses CSS Media Queries to present different layouts based on screen sizes/type of screen.
We have a pre-determined ‘break point’ on our pages, meaning any user visiting from a device with a viewport width of 600px or wider (like someone viewing your page on an iPad, for example) will be served the Desktop version of your page, and anyone visiting from a device with a viewport smaller than 600px, like an iPhone 5, will be served the mobile version of your page.
I hope this information is helpful, Daniela. As you get started with Mobile Responsive, I’d recommend checking out this handy guide here: http://documentation.unbounce.com/hc/en-us/articles/203788184-Working-With-the-Page-Builder-#content2. If you have any other questions, definitely reach out to us at firstname.lastname@example.org. We’d be happy to chat further!