Set default css for new heroku deployments

During yesterday's stream, it was brought to my attention that Heroku
deployments with the default blank value set for custom CSS causes a
bizarre appearance (all black and white with missing UI elements).

Setting the custom css variable to the default seems to fix this
problem.

app.json

@@ -157,7 +157,7 @@
     },
     "WHOOGLE_CONFIG_STYLE": {
         "description": "[CONFIG] Custom CSS styling (paste in CSS or leave blank)",
-        "value": "",
+        "value": ":root { /* LIGHT THEME COLORS */ --whoogle-background: #d8dee9; --whoogle-accent: #2e3440; --whoogle-text: #3B4252; --whoogle-contrast-text: #eceff4; --whoogle-secondary-text: #70757a; --whoogle-result-bg: #fff; --whoogle-result-title: #4c566a; --whoogle-result-url: #81a1c1; --whoogle-result-visited: #a3be8c; /* DARK THEME COLORS */ --whoogle-dark-background: #222; --whoogle-dark-accent: #685e79; --whoogle-dark-text: #fff; --whoogle-dark-contrast-text: #000; --whoogle-dark-secondary-text: #bbb; --whoogle-dark-result-bg: #000; --whoogle-dark-result-title: #1967d2; --whoogle-dark-result-url: #4b11a8; --whoogle-dark-result-visited: #bbbbff; }",
         "required": false
     }
   }