Part of your problem might be a glitch in the files for 1.5.6a. It has been replaced with 1.5.6b for a reason. Lots of little bugs.
As to the responsive_classic, I suggest getting two mods to create a new template as the second step (first being the quick move to 1.5.6b). Color Change and Clone a Template mods allow you to change the way the colors are done and, then, clone the result to a template with your name on it.
Along the way, you will want to make sure the stylesheets are set to the proper permission and know that just changing something in the web toolkit part of a browser will not make the change permanent. File permissions (other than the configure.php files) should be 644 while folders may depend on your system. Generally 755 for folders.
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