[Glitch] Fix tiny checkboxes and radio buttons in Safari

Port 51a956b6bc to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/mastodon/forms.scss

@@ -501,6 +501,8 @@ code {
 
     input[type='radio'] {
       accent-color: var(--color-text-brand);
+      width: 15px;
+      height: 15px;
     }
   }
 
@@ -534,6 +536,8 @@ code {
   label.checkbox {
     input[type='checkbox'] {
       accent-color: var(--color-text-brand);
+      width: 15px;
+      height: 15px;
     }
   }