css: use Exo as headers font, misc branding improvements

docs/source/_static/css/custom.css

@@ -0,0 +1,15 @@
+@import url('https://fonts.googleapis.com/css2?family=Exo:ital,wght@0,100..900;1,100..900&family=Inter:ital,opsz,wght@0,14..32,100..900;1,14..32,100..900&family=K2D:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;1,100;1,200;1,300;1,400;1,500;1,600;1,700;1,800&family=Ubuntu+Mono:ital,wght@0,400;0,700;1,400;1,700&display=swap');
+
+.rst-content .toctree-wrapper > p.caption, h1, h2, h3, h4, h5, h6, legend, .wy-nav-side {
+    font-family: Exo;
+}
+
+.wy-side-scroll {
+    font-size: 18px;
+}
+
+.wy-side-nav-search {
+    background-image: linear-gradient(150deg,#004B8D 0%,#2990EA 100%);
+    padding-top: 2em;
+    padding-bottom: 2.5em;
+}

docs/source/conf.py

@@ -39,6 +39,10 @@
 templates_path = ["_templates"]
 exclude_patterns = []
 
+html_css_files = [
+    'css/custom.css',
+]
+
 # add_module_names = False
 modindex_common_prefix = ["pyBADA."]