<NME> main.scss
<BEF> // OVERVIEW

* {
  box-sizing: border-box;
}

body {
  max-width: 1200px;
  padding: 1em 2em;
  margin: 0 auto;
}

// PREVIEW AREA

// TYPOGRAPHY

::selection {
  background-color: $color--highlight;
  color: $color--dark;
}

    margin-bottom: 1em;

    iframe {
      outline: #ccc solid 1px;
      width: 100%;
      min-height: 40vh;
      overflow: scroll;
  background-color: $color--highlight;
  padding: .2em;

    input {
      width: 100%;
      font-size: 150%;
      margin-top: 1em;
      padding: .2em;
    }
  margin-left: 2em;

  @media (max-width: 600px) {
    margin-left: 0em;
  }
}

h2 {
  color: $color--primary;
  height: 50vh;

  iframe {
    outline: #ccc solid 1px;
    position: absolute;
    top: 0; left: 0;
    width: 100%;
  font-size: 0.75em;
}

// PREVIEW AREA

.preview-area{
  display: flex;
  flex-wrap: wrap;
  width: 100%;
  justify-content: space-between;

  .iframe-preview {
    position: relative;
    width: 49%;
    margin-bottom: 1em;

    @media (max-width: 600px) {
      width: 100%;
      display: block;
    }

    iframe {
      outline: 1px solid black;
      width: 100%;
      min-height: 40vh;
      overflow: scroll;
      background-color: white;
    }

    input {
      width: 100%;
      margin-top: 1em;
      font-size: 1em;
      padding: .4em;
      font-family: 'Exo 2';
      border: none;
    }
  }
}

.logo {
  max-width: 260px;
}

.resize-note {
  float: right;
}

.change-note {
  position: absolute;
  top: -.5em;
  left: 1em;

  .arrow-up {
    transform: rotate(180deg);
  }
}

.arrow-up {
  width: 1em;
}

// overlay area
.overlay-area {
  position: relative;
  overflow: auto;
  // width: 10px;
  min-height: $iframe-height;
  resize: both;
  cursor: nwse-resize;

  iframe {
    outline: 1px solid $color--primary;
    position: absolute;
    top: 0; left: 0;
    width: 100%;
    height: 100%;
    background-color: white;
    pointer-events: none;

    &:nth-child(2) {
      mix-blend-mode: difference;
    }
  }
}
<MSG> fixed bug where second box didn't work

<DFF> @@ -1,13 +1,53 @@
-// OVERVIEW
+// VARS
+
+$color--secondary: #4bf;
+$color--bg: #1a416d;
+
+// BASE LAYOUT
 
 * {
   box-sizing: border-box;
 }
 
 body {
+  color: white;
   max-width: 1200px;
   padding: 1em 2em;
   margin: 0 auto;
+  font-size: 20px;
+  line-height: 1.5;
+  font-family: sans-serif;
+  background-color: $color--bg;
+  font-weight: 100;
+}
+
+footer {
+  padding: 1em 0;
+  text-align: center;
+}
+
+a {
+  color: $color--secondary;
+}
+
+// TYPOGRAPHY
+
+code {
+  background: $color--secondary;
+  font-size: .8em;
+  padding: .2em;
+}
+
+h2 {
+  color: $color--secondary;
+}
+
+small {
+  margin-bottom: 2em;
+  display: block;
+  font-style: italic;
+  font-size: 0.75em;
+  margin-top: -2em;
 }
 
 // PREVIEW AREA
@@ -22,7 +62,7 @@ body {
     margin-bottom: 1em;
 
     iframe {
-      outline: #ccc solid 1px;
+      // outline: #ccc solid 1px;
       width: 100%;
       min-height: 40vh;
       overflow: scroll;
@@ -31,7 +71,7 @@ body {
 
     input {
       width: 100%;
-      font-size: 150%;
+      font-size: 120%;
       margin-top: 1em;
       padding: .2em;
     }
@@ -47,7 +87,7 @@ body {
   height: 50vh;
 
   iframe {
-    outline: #ccc solid 1px;
+    // outline: #ccc solid 1px;
     position: absolute;
     top: 0; left: 0;
     width: 100%;

fixed bug where second box didn't work