style.css

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
html {
    font-family: 'IBM Plex Mono', monospace;
    font-size: 62.5%;
}
h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 20px;
}
h2 {
    font-size: 2.5rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 10px;
}
hr {
    margin: 20px 0;
    height: 2px;
    background-color: black;
    border: none;
}
input {
    width: 100%;
    margin: 10px 0;
    padding: 8px;
    border: 1px solid black;
    border-radius: 10px;
}
input:focus {
    border: 1px solid #c4c4c4;
    outline: none;
}
label {
    display: flex;
    flex-direction: column;
    align-items: center;
    font-size: 2rem;
}
label > span {
    font-size: 1.5rem;
}
button {
    width: 100%;
    padding: 8px 0;
    background: #c4c4c4;
    border: 1px solid black;
    border-radius: 10px;
    font-size: 1.5rem;
}
button:hover {
    cursor: pointer;
}
button:focus {
    border: 1px solid black;
    outline: none;
}
body {
    display: flex;
    flex-direction: column;
    height: 100vh;
    justify-content: center;
    align-items: center;
}
main {
    border: 1px solid black;
    width: 60%;
    padding: 20px;
    display: flex;
    flex-direction: column;
    justify-content: center;
}
.encrypt_container,
.decrypt_container {
    display: flex;
    flex-direction: column;
}
.encrypt_form,
.decrypt_form {
    display: flex;
    flex-direction: column;
    align-items: center;
    width: 100%;
}