use span instead of div (so it won't modify the height of the panel when the warning is displayed)

src/app/settings-tab.js

@@ -36,6 +36,7 @@ var css = csjs`
   }
   .compilationWarning extends ${styles.warningTextBox} {
     margin-top: 1em;
+    margin-left: 0.5em;
   }
 }
 `
@@ -62,7 +63,7 @@ function settingsTab () {
       <div class="${css.crow}">
         <div><input class="${css.col1}" id="autoCompile" type="checkbox" checked></div>
         <span class="${css.checkboxText}">Auto Compile</span>
-        <div id="warnCompilationSlow" class="${css.compilationWarning}"></div>
+        <span id="warnCompilationSlow" class="${css.compilationWarning}"></span>
       </div>
       </div>
       <div class="${css.crow}">