Fix up the logo + theme

docs/_static/css/theme-mod.css

@@ -0,0 +1,9 @@
+@import url("theme.css");
+
+.wy-side-nav-search > a img.logo {
+    width: 100%;
+}
+
+.wy-side-nav-search {
+    background: none;
+}

docs/conf.py

@@ -141,6 +141,7 @@ html_logo = 'design/payments-logo-plain.svg'
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ['_static']
+html_style = 'css/theme-mod.css'
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied