style.css

/* Parent Container */
.parent {
    display: flex;
    justify-content: center; /* Center horizontally */
    align-items: center; /* Center vertically */
    height: 100vh; /* Full height of the screen */
    background-color: lightgray;
}

/* Child Box */
.container {
    width: 300px;
    height: 450px;
    border: 5px solid black; /* Border */
    background-color: white;
    border-radius: 10px; /* Optional */
}
.txt {
    margin: 10px;
    width: 200px;
    height: 50px;
    font-size: 40px;
    text-align: right;
    border: 5px solid rgb(28, 27, 27);

}
.box {
    width: 50px;
    height: 50px;
    margin: 10px;
    font-size: 30px;
    border: 5px ridge rgb(28, 27, 27);
    border-radius: 5px;

}
#op {
    background-color: #e7ef0e;
}
#op:hover {
    background-color: aliceblue;
}
h1 {
    text-align: center;
}