style.css

@import url(https://fonts.googleapis.com/css2?family=Monoton&display=swap);
@import url(https://fonts.googleapis.com/css2?family=Roboto+Mono&display=swap);

body {
    padding: 25px;
    background-color: white;
    color: #222222;
    font-size: 25px;
}
.dark-mode {
    background-color:#222222;
    color: white;
}
#navbar {
    position: fixed;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: row;
    flex-wrap: wrap;
    display: flex;
}
#toggle {
    margin-right: 30px;
    margin-left: 73%;
    background-color: inherit;
    height: 40px;
    width: 40px;
    border-radius: 25%;
    text-align: left;
    border: none;
}
.button {
    font-size: 25px;
    margin-left: -20%;
    margin-top: -12.5%;
}
.logo {
    font-family: "Monoton";
    text-decoration: none;
    color: #1687a7;
    font-size: 50px;
}
.letter {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    overflow: auto;
    margin: auto;
    width: 1160px;
    height: 800px;
    background-color:#1687a7;
    overflow: hidden;
    border: none;
    border-color: #1687a7;
    border-width: 5px,5px,5px,5px;
    border-radius: 20px;
}
#sender {
    margin-left: 2%;
    margin-top: 2%;
    height: 35px;
    width: 400px;
    background-color: #eeeeee;
    border: none;
    border-color: #eeeeee;
    border-width: 1%,1%,1%,1%;
    border-radius: 5px;
    align-items: right;
    text-overflow: clip;
    font-size: 30px;
}
#message {
    margin-left: 2%;
    width: 95%;
    height: 500px;
    background-color: #eeeeee;
    border: none;
    border-radius: 5px;
    resize: none;
    padding: 0;
    line-height: 1em;
    text-overflow: clip;
    font-size: 30px;
}
.submit {
    background-color: #0b4252;
    color: #eeeeee;
    font-family: "Roboto Mono";
    font-size: 30px;
    font-weight: bolder;
    margin-left: 82.5%;
    margin-bottom: 30px;
    border-style: none;
    border-radius: 20px;
    width: 170px;
    height: 140px;
}