I modified templates to include a base.jade, and to alter blocks defined in a base with block append.

But jade behave that that blocks are actually being appended to theirs places, but they are also being included to the end of a file. So, I had to manually modify resulted .jade.go files.

web/templates/base.jade

@@ -18,7 +18,6 @@ html(lang="en")
 			nav
 				a(href=mainSite title="Arav's dwelling") Back to main website
 				block header
-					h1 Upload
 		block body
 		footer
 			| 2022 Arav <#[a(href="mailto:me@arav.top") me@arav.top]>

web/templates/error404.jade

@@ -1,6 +1,8 @@
 :go:func Error404(mainSite string)
 
-include base/top.jade
+include base.jade
+
+block append head
 	style(type="text/css").
 		#error {
 			font-size: 3.5rem;
@@ -9,11 +11,11 @@ include base/top.jade
 			margin: 6rem 0; }
 
 		#error h1 { font-size: 8rem; }
-include base/body.header.jade
+
+block append header
 	h1 404
 
+block append body
 section#error
 	h1 404
 	| Nod Found xD
-
-include base/body.footer.jade

web/templates/index.jade

@@ -1,9 +1,11 @@
 :go:func Index(mainSite string, storageCapacity, storageUsed int64, keepForHours int, fileMaxSize, storageUsedStr, storageCapacityStr, storageAvailableStr string)
 
-include base/top.jade
-include base/body.header.jade
+include base.jade
+
+block append header
 		h1 Upload
 
+block body
 	section#rules.center
 		h2 Rules
 		ul
@@ -34,5 +36,3 @@ section
 		p Upload logs include: access time, IP-address, name of a file it was uploaded with, a SHA-256 hash of the file, download name*, size of the file in bytes, User-Agent.
 		p Each download also being logged and include: access time, IP-address, name of a file it was requested with, download name*, User-Agent.
 		p *Download name is a salted SHA-256 hash of the file encoded using base64 raw URL encoding. The hash is being salted to make useless any attempt of bruteforcing.
-
-include base/body.footer.jade

web/templates/nospace.jade

@@ -1,6 +1,8 @@
 :go:func ErrorNoSpace(mainSite string)
 
-include base/top.jade
+include base.jade
+
+block append head
 	style(type="text/css").
 		#error {
 			font-size: 3.5rem;
@@ -9,10 +11,10 @@ include base/top.jade
 			margin: 6rem 0; }
 
 		#error h1 { font-size: 6rem; }
-include base/body.header.jade
+
+block append header
 	h1 :(
 
+block append body
 section#error
 	h1 Not enough space left
-
-include base/body.footer.jade

web/templates/uploaded.jade

@@ -1,9 +1,11 @@
 :go:func Uploaded(mainSite, downloadLink string, keepForHours int)
 
-include base/top.jade
-include base/body.header.jade
+include base.jade
+
+block append header
 	h1 Upload
 
+block append body
 	section#file
 		h2 Your link
 		center
@@ -11,5 +13,3 @@ section#file
 		center It will be available for next #{keepForHours} hours.
 		center
 			a(href="/") Back to index page
-
-include base/body.footer.jade