style: increase doc body max width (#1485)

<!-- please provide a detailed description of the changes made in this
pull request. -->

Increase documentation website body `max-width` in order to improve the
render on large screen but keeping the main column width under the
recommended `max-width` for staying comfortable to read (UX).


<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

misc/docusaurus/src/css/custom.css

@@ -35,6 +35,8 @@
   --ifm-links-hover-background-color: var(--ifm-color-primary-light);
   --ifm-color-secondary: var(--ifm-color-primary-light);
   --ifm-color-white: var(--ifm-color-primary);
+
+  --content-max-w: 50rem;
 }
 
 /* For readability concerns, you should choose a lighter palette in dark mode. */
@@ -61,7 +63,7 @@
 body {
   margin-left: auto;
   margin-right: auto;
-  max-width: 84rem;
+  max-width: 100rem;
   padding-inline: 1rem;
 }
 
@@ -114,6 +116,10 @@ pre code {
   }
 }
 
+.theme-doc-markdown {
+  max-width: var(--content-max-w, 700px);
+}
+
 .navbar-sidebar--show ~ .main-wrapper {
   filter: blur(2px);
 }
@@ -126,6 +132,7 @@ pre code {
 .pagination-nav {
   grid-template-columns: repeat(1, 100%);
   grid-template-rows: repeat(2, 1fr);
+  max-width: var(--content-max-w, 700px);
 }
 .pagination-nav__link--next {
   grid-column: 1/2;