Improve font rendering

assets/_markdown.scss

@@ -16,7 +16,7 @@ $block-border-radius: 0.15rem;
   }
 
   b, optgroup, strong {
-    font-weight: 400;
+    font-weight: 700;
   }
   
   a {
@@ -28,7 +28,7 @@ $block-border-radius: 0.15rem;
   }
 
   code {
-    font-family: 'Roboto Mono', monospace;
+    font-family: 'Oxygen Mono', monospace;
   }
 
   p code {

assets/_variables.scss

@@ -21,7 +21,7 @@ $gray-800: #343a40;
 $gray-900: #212529;
 $black:    #000;
 
-$color-link: #4092f1;
+$color-link: #004ed0;
 $color-visited-link: #8440f1;
 
 $body-background: white;

assets/book.scss

@@ -4,7 +4,7 @@
 
 html {
   font-size: $font-size-base;
-  letter-spacing: .3px;
+  letter-spacing: .33px;
 }
 
 html, body {
@@ -15,9 +15,14 @@ html, body {
 body {
   color: $body-font-color;
   background: $body-background;
+
   font-family: 'Oxygen', sans-serif;
   font-weight: $body-font-weight;
 
+  text-rendering: optimizeLegibility;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+
   box-sizing: border-box;
   * {
     box-sizing: inherit;