fix: show logo in docs navbar; remove blockquote border in README

- Add docs/stylesheets/extra.css: white pill background on .md-logo img
  so the dark navy hexagon is visible on the indigo navbar
- Restore logo: assets/logo_small.png in mkdocs.yml
- Wire extra_css: [stylesheets/extra.css] in mkdocs.yml
- Replace README blockquote with italic text to eliminate the floating
  left-border line that appeared above the right-aligned logo image

Author: athammad

README.md

@@ -1,6 +1,6 @@
 <img src="docs/assets/logo_small.png" alt="OnlineCML" width="180" align="right"/>
 
-> Causal inference for the real world — one observation at a time.
+*Causal inference for the real world — one observation at a time.*
 
 [![CI](https://github.com/athammad/onlinecml/actions/workflows/ci.yml/badge.svg)](https://github.com/athammad/onlinecml/actions/workflows/ci.yml)
 [![Coverage](https://img.shields.io/badge/coverage-97%25-brightgreen)](https://github.com/athammad/onlinecml)

docs/stylesheets/extra.css

@@ -0,0 +1,6 @@
+/* Give the header logo a white pill background so it's visible on the indigo navbar */
+.md-header__button.md-logo img {
+  background: white;
+  border-radius: 6px;
+  padding: 3px;
+}

mkdocs.yml

@@ -6,6 +6,7 @@ repo_name: athammad/onlinecml
 
 theme:
   name: material
+  logo: assets/logo_small.png
   favicon: assets/logo_small.png
   palette:
     - scheme: default
@@ -92,6 +93,9 @@ markdown_extensions:
   - pymdownx.arithmatex:
       generic: true
 
+extra_css:
+  - stylesheets/extra.css
+
 extra_javascript:
   - javascripts/mathjax.js
   - https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js