So basically, you have one div areas with width set:
Code:
<div class="header2-left" style="width:740px;">
<div class="header2-right">
What you need to realize is, you're viewing a desktop type style on a mobile phone. So if you open this site on a pc, like me for example it looks fine, login is at top right. Look at the code though, in the top div class its using a style reference, setting the width to 740px, if you resize your browser smaller (or view on mobile as you did) you will notice it then goes to the line below. You'll need to either remove the 740width being set OR set to 75% then right div to 25% OR 50/50%. You could also set a container div, this is a perfect example:
https://vborg.vbsupport.ru/showthread.php?t=228319 even though its dealing with a header/logo, the css and div you can reference to see how it was done then repeat on your area
.