index.css

* {
    padding: 0;
    margin: 0;
    border: none;
}

html,
body {
    background: white;
    font-size: 18px;
    color: #444;
    overflow-x: hidden;
    /* overflow: hidden; */
}

.main_layout {
    display: grid;
    grid-template-columns: 36rem 1fr;
    width: 100vw;
    height: 100vh;
    overflow: hidden;
}

.main_layout > * {
    height: 100vh;
}

#htmlContainer {
    position: fixed;
    top: calc(100% - 72px);
    right: 0px;
    z-index: 999;
    width: 100%;
    height: 100%;
    overflow: hidden;
    transition: all 0.35s ease-in-out;
    box-shadow: 0px 0px 5px 0px rgba(0, 0, 0, 0.15);
}

#render {
    height: 100%;
    overflow-y: auto;
}

#code {
    outline: 1px solid red;
    height: 100%;
}

.toolbar {
    position: fixed;
    top: 0;
    right: 0;
    padding: 1rem;
    z-index: 999;
}

.CodeMirror {
    width: 100%;
    height: 100%;
}

#toggleContainer {
    display: flex;
    justify-content: center;
    align-items: center;
}

input[type=checkbox] {
    height: 0;
    width: 0;
    visibility: hidden;
}

label {
    cursor: pointer;
    text-indent: -9999px;
    width: 48px;
    height: 32px;
    /* box-shadow: inset 0px 0px 0px 1px rgba(0, 0, 0, 0.15); */
    background: moccasin;
    display: block;
    border-radius: 20px;
    position: relative;
    margin: 0px;
    padding: 0px;
}

label:after {
    content: '';
    position: absolute;
    top: 4px;
    left: 4px;
    width: 24px;
    height: 24px;
    background: white;
    border-radius: 16px;
    transition: 0.2s;
    box-shadow: 0px 0px 1px rgba(0, 0, 0, 0.35), 0px 8.71728px 17.2408px rgba(0, 0, 0, 0.0185187), 0px 2.76435px 5.19761px rgba(0, 0, 0, 0.0225848), 0px 1.18477px 2.15882px rgba(0, 0, 0, 0.0264039), 0px 0.409114px 0.780803px rgba(0, 0, 0, 0.04);
}

input:checked+label {
    background: #a3be8c;
}

input:checked+label:after {
    left: calc(100% - 4px);
    transform: translateX(-100%);
}

label:active:after {
    width: 32px;
}