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

@@ -1,16 +1,18 @@
 :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
 
-section#rules.center
+block body
+	section#rules.center
 		h2 Rules
 		ul
 			li Max. file size is #{fileMaxSize}.
 			li It will be kept for #{keepForHours} hours.
 			li Anything you upload should comply with Russian Federation's law. Generally speaking, anything illegal, like CP, extremist literature etc., is forbidden.
-section#used-space.center
+	section#used-space.center
 		h2 Free space
 		div
 			span #{storageUsedStr}
@@ -18,21 +20,19 @@ section#used-space.center
 			span #{storageCapacityStr}
 		div
 			| #{storageAvailableStr}
-section#upload.center
+	section#upload.center
 		h2 Upload
 		form(action="/" method="POST" enctype="multipart/form-data")
 			input(type="file" name="file" multiple=false)
 			button(type="submit") Upload
-section
+	section
 		p.center You can use cURL to upload a file: #[code curl -F 'file=@somefile.ext' https://upload.arav.top]
 		p.center Over I2P: #[code curl --proxy 127.0.0.1:4444 -F 'file=@somefile.ext' http://upload.arav.i2p]
 		p.center A resulted link looks like this: #[code /f/base64rawURL(sha256)/filename.ext].
 		p.center filename.ext is mandatory. It is a name the file will be retrieved with.
-section
+	section
 		h2 Privacy statements
 		p I WILL cooperate with law enforcements and provide them with logs, guess I shouldn't clarify why. Abuses should be sent to #[a(href="mailto:admin@arav.top") admin@arav.top].
 		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

@@ -1,15 +1,15 @@
 :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
 
-section#file
+block append body
+	section#file
 		h2 Your link
 		center
 			a(href=downloadLink) #{downloadLink}
 		center It will be available for next #{keepForHours} hours.
 		center
 			a(href="/") Back to index page
-
-include base/body.footer.jade