style.css

body{
    padding : 0 ;
    margin : 0 ;
    font-family: sans-serif;
}

.container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 100vh;
    background-color: rgb(204, 217, 16);

}

h1{
    color: black;
    text-align: center;
}
.digit {
    font-size: 150px;
    color: #fff;
}
.txt {
    font-size: 30px;
    color: #fffcd6;
}
.btn {
    width: 100px;
    padding: 10px 15px;
    margin: 0px 20px;
    border-top-right-radius: 10px;
    border-bottom-left-radius: 10px;
    border-bottom-right-radius: 4px;
    border-top-left-radius: 4px;
    cursor: pointer;
    font-size: 20px;
    transition: 0.5s;
    color: white;
    font-weight: 500;
}
 
#start {
    background-color: #009779;
}
 
#stop {
    background-color: #0e85fc;
}
 
#reset {
    background-color: #c91400;
}