Xhtml 730px container and 680px wrap

First of all: our responsive usage. I see you are using site-only-content layout. These are our codes making that layout:

.site-only-content .container { max-width: 620px; }
@media (min-width: 1200px) { .site-only-content .container { max-width: 770px; } }
@media (min-width: 768px) and (max-width: 979px) { .site-only-content .container { max-width: 476px; } }

First `.site-only-content .container { max-width: 620px; }` section is for Default displays(980px and up),
Second `@media (min-width: 1200px) { .site-only-content .container { max-width: 770px; } }` section is for Large displays(1200px and up).

If i understand you correct, you want fixed 730px width site for Default and Large displays. This code should make it:

.site-only-content .container { max-width: 730px; }
@media (min-width: 1200px) { .site-only-content .container { max-width: 730px; } }

I dont understand what you mean by a wrap included embed content with 680px width.. What is that wrap’s ID? is it special ID or you mean one of FirmaSite wraps? You need to define this

For centering: you can just click text center button on your editor.

For videos, i suggest you to use `flex-video` class. Like this:

<div class="flex-video">
VIDEO CODE HERE
</div>

Thank you for reporting plugin error. It was a minor bug that prevent plugin working in old php versions (older then php5.3). I updated plugin, please uninstall and install it again.

Btw this is center button:

I dont understand most of your questions but those seems css customizations.

If you dont know how to implement css, you should start to learn how to use css first. Those can be guide for you:

http://www.htmldog.com/guides/css/beginner/

http://www.htmldog.com/guides/css/intermediate/

http://www.htmldog.com/guides/css/advanced/

You should start from learning basic things before going to customize an advanced theme