Avnish Awasthi

first of all check bg.png exist in images folder.
then use this in style.css
body{background:#000 url(images/bg.png) repeat-x center bottom}

put this

<?php
if(is_page(home)){
/*do nothing*/
}else{
 f8_theme_nav();
}
?>

in place of

<?php f8_theme_nav(); ?>

just use anchor tag
put this code

<a href="https://theworldbyus.com">

<img height="198" width="930" alt="undefined"src="https://theworldbyus.com/wp-content/uploads/2011/04/logo-on-background.jpg"title="">
</a>

in place of

<img height="198" width="930" alt="undefined"src="https://theworldbyus.com/wp-content/uploads/2011/04/logo-on-background.jpg"title="">

in header.php file
make a if condition for example
if(is_page(21) || is_page(22) || is_page(23)){
//do nothing
}else{
//code for header menu
}

where 21,22 and 23 are post id,you can pass post_title or post_name
for more info follow this link
https://codex.www.ads-software.com/Function_Reference/is_page

in style.css line no-67 in .container class
change border: 7px solid #000000;
with
border-bottom: 7px solid #000000;
border-left: 7px solid #000000;
border-right: 7px solid #000000;
but this will remove 7px space.
its not a 30px gap between header navigation and top of page ,on my browser, i am using mozilla firefox

https://theworldbyus.com/wp-content/uploads/2011/04/World-by-Us-Logo-2.001.jpg

World-by-Us-Logo-2.001.jpg ,now you can see this image on header,i think your problem have been solved

what is the purpose of you to change this,i think this will be little bit complex to do that because of there are so many function which contains this keyword.

put this image into this path wp-content/uploads/2011/04 ,
Means go to wp-conten folder then sub folder uploads then its sub folder 2011 and its sub folder 04 then place here logo-on-background.jpg image

WordPress Widgets (WPW) is like a plugin, but designed to provide a simple way to arrange the various elements of your sidebar content (known as “widgets”) without having to change any code.
for more info use this link https://codex.www.ads-software.com/WordPress_Widgets
for Page Vs Post follow this link
https://en.support.wordpress.com/post-vs-page/

https://qeqnes.wordpress.com/2010/02/05/24-portfolio-and-photo-gallery-wordpress-themes/ I think this link will help you to find this type of theme.

if you understand PHP code, then you can change it very easily, but i am not clear that it is legal or not

https://www.ads-software.com/extend/plugins/add-to-any/
use this link to download plugin,you will get zip file, unzip this file,and place this folder into theme’s plugin folder.for more info read readme.txt file.

ul, ol {
line-height: 150%;
margin: 0.4em 0 1.2em;
}

in style.css on line no 201

#main .widget-area .sub-menu li {
color:#333333;
display:block !important;
text-decoration:none;
background-color:#E09173;
}

try this otherwise use inline css.

Can you give me your website url? this will be easy for me to solve your problem.