Fix invalid CSS rules (#9039)

ui/app/components/app/multiple-notifications/index.scss

@@ -16,7 +16,6 @@
     position: relative;
     width: 100%;
     height: 100%;
-    visibility: none;
 
     .fa-sm {
       display: initial;

ui/app/components/app/permission-page-container/index.scss

@@ -129,8 +129,8 @@
   }
 
   &__tooltip-body {
-    display: 'flex';
-    flex-direction: 'column';
+    display: flex;
+    flex-direction: column;
   }
 
   &__bold-title-elements {

ui/app/components/app/sidebars/sidebar-content.scss

@@ -34,7 +34,6 @@
     .page-container__bottom {
       display: flex;
       flex-direction: column;
-      flex-flow: space-between;
       height: 100%;
     }
 

ui/app/components/app/signature-request/signature-request-footer/index.scss

@@ -9,11 +9,11 @@
     border-radius: 3px;
   }
 
-  button:first-child() {
+  button:first-child {
     margin-left: 1rem;
   }
 
-  button:last-child() {
+  button:last-child {
     margin-right: 1rem;
   }
 }

ui/app/css/itcss/components/pages/permission-approval.scss

@@ -5,7 +5,7 @@
 }
 
 .permission_approval_origin {
-  font-weight: 999;
+  font-weight: 900;
   margin-top: 16px;
   word-wrap: break-word;
 }

ui/app/css/variables/colors.scss

@@ -1,5 +1,5 @@
 // These are the colors of the MetaMask design system
-// Only design system colors should be added, no superfulous variables
+// Only design system colors should be added, no superfluous variables
 // See https://bit.ly/32mnoja (link to figma design system)
 $Blue-000: #eaf6ff;
 $Blue-100: #a7d9fe;