clean up navbar icons

src/css/custom.css

@@ -46,7 +46,7 @@ html[data-theme='dark'] {
   height: 24px;
   display: flex;
   background-color: var(--ifm-navbar-link-color);
-  mask-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12'/%3E%3C/svg%3E");
+  mask-image: url('/img/github-icon.svg');
   transition: background-color var(--ifm-transition-fast)
     var(--ifm-transition-timing-default);
 }
@@ -63,7 +63,7 @@ html[data-theme='dark'] {
   height: 24px;
   display: flex;
   background-color: var(--ifm-navbar-link-color);
-  mask-image: url("data:image/svg+xml,%3C%3Fxml version='1.0' encoding='UTF-8'%3F%3E%3Csvg id='Layer_1' data-name='Layer 1' xmlns='http://www.w3.org/2000/svg' version='1.1' viewBox='0 0 359.7 359.7'%3E%3Cdefs%3E%3Cstyle%3E .cls-1 %7B fill: %23000; stroke-width: 0px; %7D %3C/style%3E%3C/defs%3E%3Cpath class='cls-1' d='M314.5,138.3l-46.6,45.6c2.6,8.3,3.9,17.1,3.9,26,0,24-9.6,46.6-27,63.6-17.4,17-40.5,26.3-65.1,26.3s-47.7-9.4-65.1-26.3c-17.4-17-27-39.6-27-63.6s1.3-17.7,3.9-26l-46.7-45.6c-11.8,21.3-18.6,45.7-18.6,71.6,0,82.8,68.7,149.8,153.4,149.8s153.4-67.1,153.4-149.8-6.7-50.3-18.6-71.6h0Z'/%3E%3Cpolygon class='cls-1' points='149.1 239.8 210.4 239.8 210.4 144.5 314.9 42.4 271.5 0 179.8 89.6 88 0 44.6 42.4 149.1 144.4 149.1 239.8'/%3E%3C/svg%3E");
+  mask-image: url('/img/yearn-link-icon.svg');
   transition: background-color var(--ifm-transition-fast)
     var(--ifm-transition-timing-default);
 }