Improve/add error messages to look better visually

- Have not tested everywhere, but should work okayish

static/styles.scss

@@ -59,6 +59,7 @@ body, html {
   #img-logo {
     height: 100%;
     box-sizing: border-box;
+
     img {
       max-width: 100%;
       max-height: 80px;
@@ -145,12 +146,12 @@ nav, footer {
 }
 
 form {
-  margin: 0 auto;
+  margin: 1em auto;
   width: fit-content;
 
   &.login-form {
     border: 1px solid darkblue;
-    padding: 10px
+    padding: 0.7em;
   }
 
   .field {
@@ -308,6 +309,7 @@ form {
 
   .post-author {
     margin-top: 1em;
+    margin-bottom: 0.5em;
     font-size: 0.8em;
     border-bottom: 1px solid grey;
     padding-bottom: 0.8em;
@@ -350,6 +352,7 @@ form {
 
 .new-users, .statistics {
   margin-top: 0 !important;
+
   > div {
     border: 1px solid grey;
     padding: 0.2em;
@@ -366,3 +369,14 @@ form {
   min-height: 235px;
   margin: 1em;
 }
+
+span.error-message {
+  margin: 0.5em;
+  border: 1px solid red;
+  padding: 0.3em;
+
+  &.center-message {
+    margin: 0 auto;
+    display: table;
+  }
+}