project-codepen/src/index.css

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
    'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
    sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

code {
  font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
    monospace;
}

.top-pane {
    background-color: hsl(225, 6%, 25%);
}
  
.pane {
    height: 50vh;
    display: flex;
}

.editor-container {
    flex-grow: 1;
    flex-basis: 0;
    display: flex;
    flex-direction: column;
    padding: .5rem;
    background-color: hsl(225, 6%, 25%);
}
  
.editor-container.collapsed {
    flex-grow: 0;
}

.editor-container.collapsed .CodeMirror-scroll {
    position: absolute;
    overflow: hidden !important;
}
  
.expand-collapse-btn {
    margin-left: .5rem;
    background: none;
    border: none;
    color: white;
    cursor: pointer;
}
  
.editor-title {
    display: flex;
    justify-content: space-between;
    background-color: hsl(225, 6%, 13%);
    color: white;
    padding: .5rem .5rem .5rem 1rem;
    border-top-right-radius: .5rem;
    border-top-left-radius: .5rem;
}
  
.CodeMirror {
    height: 100% !important;
}
  
.code-mirror-wrapper {
    flex-grow: 1;
    border-bottom-right-radius: .5rem;
    border-bottom-left-radius: .5rem;
    overflow: hidden;
}