Sans-serif, plenty of whitespace and a single blue accent — goblog's minimal theme.

3a497aa1690d8c3f71ff2e3784aa1d6752f6292793593e533c789100417bfdc1Install it from your own goblog under Admin → Themes.
Sans-serif, plenty of whitespace and a single blue accent. This is the theme that shipped compiled into goblog as minimal up to 0.6.x, published as a directory theme so it can be installed and updated on its own.
From your goblog: Admin → Themes → Browse → Minimal → Install, then Activate. Requires goblog 0.7.0 or newer (earlier releases have a built-in minimal that shadows an installed copy).
Upgrading a site that already used the built-in minimal: after the goblog upgrade the site renders the default theme until you install Minimal from the directory; the theme setting is left alone, so the site switches back as soon as the theme is installed.
Only the public-facing templates that differ from default (header, footer, home, post, posts, login and the page_* types) and static/css/goblog.css. Everything else — admin and wizard pages, tags, archives, search, error — renders from goblog's default theme, so it keeps up with new goblog releases automatically.
Edit the files under templates/ and static/, drop the folder into a goblog checkout as themes/installed/minimal/ (or point THEMES_INSTALLED_DIR at its parent) and set the theme setting to minimal. Templates are Go html/template; see goblog.live/docs/writing-a-theme for the contract.
Tag vX.Y.Z and publish a GitHub release; the directory picks up the tag's archive. screenshot.png at the root is shown in the listing.
minimal theme that was compiled into goblog up to 0.6.x, layered on goblog's default theme.First release as a directory theme: the public templates and CSS of the minimal theme compiled into goblog up to 0.6.x, layered on goblog's default theme. Requires goblog 0.7.0 or newer.
GoBlog
Powered by goblog v0.9.1