how to center my post title? Theme [DUENA]

Try changing your custom CSS from this:

#header .logo {
float: left;
padding: 0 0 20px 0;
max-width: 100%;
}

TO THIS:

#header .logo {
float: none;
padding: 0 0 20px 0;
max-width: 100%;
text-align: center;
}

Thank you for your reply. but nothing happens :(. I don’t know but I,ve figured out that none of any plugin works at my duena theme. I have even tried customizing my drop menus through a plugin to mega menu but nothing changes.. ? any help for this?

My apologies, I thought you wanted to center your blog title instead of post title.

To center your post title, change this

.post-title {
margin: 0;
padding: 10px 0 0 0;
font-size: 46px;
overflow: hidden;
}

To this:

.post-title {
margin: 0;
padding: 10px 0 0 0;
font-size: 46px;
overflow: hidden;
text-align: center;
}

Regarding your plugins, try this – deactivate Duena theme and activate your default WordPress twentyfourteen theme to see if any of your plugins are working.

Thank you so much for your support. I appreciate it. The title did centered and I figured out how to apply the mega menu plugin. Thank you.
Just want to ask you if you are familiar with a good plugin for mega menu ?

You are more than welcome, glad I could help.

If you want a lot of options for a mega menu, the best plugin I know of is UberMenu. This is a premium plugin but I would definitely recommend it.