Google/Blogger

Hide Poster
Layout -> Configure Blog Posts
 * deselect Posted by

Hide Powered By
/* Hide "Powered by" */ font-size: xx-small; color: white; visibility: hidden; }
 * 1) Attribution1 {

Or Edit Theme HTML, Jump to #Attribution1, and delete all of this:  ... 

Pre
pre { overflow: auto; border: 1px solid black; padding: .5em; }

horizontal scrolling: pre { overflow: auto; word-wrap: normal; white-space: pre; }

&lt;pre style="overflow: auto; word-wrap: normal; white-space: pre;"

Add CSS
body { background-repeat:no-repeat; background-size:cover; }

font-size: xx-small; color: white; visibility: hidden; }
 * 1) Attribution1 {

h2 { font-size: large; color: black; }

.descriptionwrapper { visibility: hidden; }

.blog-feeds { visibility: hidden; }

.home-link { visibility: hidden; }

pre { overflow: auto; border: 1px solid black; padding: .5em; }

img.photoframe { border: 20px solid black; }

img.thinphotoframe { border: 5px solid black; }

/* .tabs-inner .widget ul { background: none; background-color: #005A9C; }

body { background-repeat:no-repeat; background-size:cover; }

font-size: xx-small; }
 * 1) Attribution1 {

.description { font-weight:bold; }

h2 { font-size: large; color: black; }

pre { overflow: auto; border: 1px solid black; padding: .5em; }

font-size: xx-small; color: white; visibility: hidden; }
 * 1) Attribution1 {

h2 { font-size: large; color: black; }

.descriptionwrapper { visibility: hidden; }

.blog-feeds { visibility: hidden; }

.home-link { visibility: hidden; }

pre { overflow: auto; border: 1px solid black; padding: .5em; }

img.photoframe { border: 20px solid black; }

img.thinphotoframe { border: 5px solid black; }

.tabs-inner .widget ul { background: none; background-color: #005A9C; }

Hide Follow By Email
Only show on Posts:

Edit HTML: (add b:if statement)     ...    

Hide Subscribe to Post Atom
Subscribe to: Posts (Atom)

To only show on post pages:

  

Stretch Background Image
Better: /* Stretch Background Image */ body { background-repeat:no-repeat; background-size:cover; }

---

html, body { background: url('bgimage.jpg') no-repeat center center fixed; -webkit-background-size: cover; -moz-background-size: cover; -o-background-size: cover; background-size: cover; }

Chang bgimage.jpg to your url

Ref: https://www.stramaxon.com/2013/01/full-page-background-blogger.html

Hide Background on Mobile
@media only screen and (max-width: 640px){ body { background-image: none !important; } }

ref: https://theme-fusion.com/knowledgebase/how-to-hide-full-width-background-images-on-mobile/