style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    height: 100vh;
    background: #FDF8EC;
    color: #333;
    font-family: "Comfortaa", sans-serif;
    font-weight: 400;
}

#container {
    margin: 0 5%;
    height: 100%;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 30px 15px;
    border-bottom: 1px solid rgba(100, 100, 100, .5);
}

#title {
    font-weight: 300;
}

#title span {
    font-weight: 700;
}

header img {
    position: absolute;
    top: 15px;
    left: 230px;
    width: 80px;
}

#dark-mode {
    display: flex;
    justify-content: flex-end;
    align-items: center;
}

#dark-mode-text {
    margin-right: 15px;
    font-weight: 700;
}

.switch {
    position: absolute;
    margin-left: -9999px;
    visibility: hidden;
}

.switch + label {
    display: block;
    position: relative;
    cursor: pointer;
    outline: none;
    user-select: none;
}

.switch--shadow + label {
    padding: 2px;
    width: 40px;
    height: 20px;
    background: #DDD;
    border-radius: 20px;
}

.switch--shadow + label:before,
.switch--shadow + label:after {
    display: block;
    position: absolute;
    top: 1px;
    left: 1px;
    bottom: 1px;
    content: '';
}

.switch--shadow + label:before {
    right: 1px;
    background: #F1F1F1;
    border-radius: 20px;
    transition: all 0.4s;
}

.switch--shadow + label:after {
    width: 20px;
    background-color: #FFF;
    border-radius: 100%;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
    transition: all 0.4s;
}

.switch--shadow:checked + label:before {
    background: #8CE196;
}

.switch--shadow:checked + label:after {
    transform: translateX(20px);
}

#content {
    display: flex;
    justify-content: space-between;
    margin-top: 30px;
    padding: 0 15px;
}

#original-area {
    width: 48%;
    height: 100%;
}

#original-area h3 {
    padding-left: 15px;
}

#original-area textarea {
    margin: 15px 0;
    padding: 15px;
    width: 100%;
    height: 300px;
    font-family: "Comfortaa", sans-serif;
    font-size: 16px;
    resize: none;
    overflow: auto;
    border: 1px solid rgba(100, 100, 100, .5);
    border-radius: 10px;
}

#crypt-area {
    width: 48%;
    height: 100%;
}

#crypt-area h3 {
    padding-left: 15px;
}

#result {
    margin: 15px 0;
    padding: 15px;
    width: 100%;
    height: 300px;
    font-family: "Comfortaa", sans-serif;
    font-size: 16px;
    resize: none;
    overflow: auto;
    background: rgba(200, 200, 200, .1);
    border: 1px solid rgba(100, 100, 100, .5);
    border-radius: 10px;
}

button {
    cursor: pointer;
    height: 35px;
    margin-right: 15px;
    padding: 0 15px;
    background: #333;
    color: #FFF;
    border: none;
    border-radius: 5px;
    font-family: "Comfortaa", sans-serif;
    font-size: 14px;
    font-weight: 300;
}

button:active, button:hover {
    background: rgba(0, 0, 0, .6);
}

#crypt-extra {
    display: flex;
    justify-content: flex-start;
    align-items: center;
}

#copy-button {
    margin-right: 30px;
}

#warn-message {
    display: flex;
    justify-content: flex-start;
    align-items: center;
    font-size: 14px;
    font-weight: 700;
}

#warn-icon {
    width: 24px;
    height: 24px;
    margin-right: 15px;
}

footer {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    margin-top: 30px;
    height: 50px;
    background: #333;
    color: #FFF;
}

.darker-bg {
    background: rgba(0, 0, 0, .6);
    color: #FFF;
}

.dark-bg {
    background: #333;
    color: #FFF;
}

.gray-bg {
    background: #555;
    color: #FFF;
}

.gray-bg::placeholder {
    color: #CCC;
}

.white-text {
    color: #FFF;
}

.dark-button {
    background: #333;
    border: 1px solid #FFF;
    color: #FFF;
}