Blisk browser layout is responsive. It means that you can resize the width of the web content and the device content.
If you need to resize the width of web content or the device content - simply drag the gray splitter, which is located between the web and device content.
Note, that Blisk browser saves the widths of the web and mobile content. If you resize these contents and open the new tab or the new window - the sizes of these contents will be the same as you have changed before.