Fixed floating button style to more consistently center the plus sign.

parts/static/style.css

@@ -240,6 +240,9 @@ div label input {
 }
 
 .round-floating-button {
+  position: flex;
+  align-items: center;
+  justify-content: center;
   position: fixed;
   bottom: 15pt;
   right: 15pt;
@@ -248,9 +251,7 @@ div label input {
   border-radius: 20pt;
   background-color: #5E9292;
   font-size: 22pt;
-  padding-top: 8pt;
   box-shadow: 2pt 1pt 8pt black;
-  text-align: center;
 }
 
 .round-floating-button a{