style.css

body {
    background-color: rgb(24, 24, 24);
    color: white;
}
header {
    margin: 20px 0;
}
.flag {
    display: inline-block;
    margin: 10px;
    position: relative;
    width: 70px;
    height: 40px;
}
.en,
.pl {
    width: 100%;
    height: 100%;
    background-size: cover;
    background-position: center;
}
.en {
    background-image: url("./img/en.svg");
}
.pl {
    background-image: url("./img/pl.svg");
}
.input-box {
    height: 200px;
    width: 100%;
    padding: 15px;
    margin-bottom: 30px;
    background-color: rgb(50, 50, 50);
    color: white;
}
label {
    margin-top: 25px;
}
textarea, textarea:focus {
    background-color: #888;
    border: none;
    outline: none;
    width: 90%;
    padding: 5px;
    height: 165px;
    resize: none;
}
textarea::-webkit-input-placeholder, input::-webkit-input-placeholder {
    color: rgb(200, 200, 200);
}
textarea:-moz-placeholder, input:-moz-placeholder { /* Firefox 18- */
    color: rgb(200, 200, 200);
}
textarea::-moz-placeholder, input::-moz-placeholder {  /* Firefox 19+ */
    color: rgb(200, 200, 200);
}
textarea:-ms-input-placeholder, input:-ms-input-placeholder {
    color: rgb(200, 200, 200);
}
textarea::placeholder, input::placeholder {
    color: rgb(200, 200, 200);
}
.read-code {
    background-color: #ccc;
    border-radius: 500px;
    padding: 8px 30px;
    color: red;
    font-family: monospace;
    font-size: 16px;
    letter-spacing: 1px;
}
input[type="number"], input[type="number"]:focus {
    background-color: #888;
    border: none;
    outline: none;
    width: 120px;
    height: 35px;
    padding-left: 15px;
}
button, button:focus {
    margin-top: 30px;
    margin-bottom: 5px;
    width: 100%;
    height: 50px;
    border: none;
    border-radius: 15px;
    outline: none;
    background-color: rgb(33, 150, 243);
    box-shadow: 0 6px 0 rgb(21, 92, 150);
    transition: .2s ease-out;
}
button:hover {
    background-color: rgb(70, 165, 243);
    /* box-shadow: 0 6px 0 rgb(21, 92, 150); */
}
button:active {
    margin-top: 35px;
    margin-bottom: 0;
    box-shadow: 0 2px 0 rgb(90, 90, 90);
    transition: .1s ease-out;
}
button[type="submit"] {
    font-size: 18px;
}
#cipher-state {
    padding-top: 30px;
}
.my-alert {
    width: 90%;
    margin: 10px auto 0 auto;
    z-index: 100;
}
.wrong {
    box-shadow: 0 0 5px red;
}