style.css

* {
    color: black;
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    /* background: url(./bg.jpg);
    background-size: 100% 100vh;
    background-repeat: no-repeat; */
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;

}

.section {
    font-size: 2rem;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    margin-bottom: 60px;
}

.time {
    font-size: 3rem;
    margin: 15px;
}

.options {
    display: flex;
    flex-direction: row;
    margin: 20px;
    width: 50vw;
    justify-content: space-around;
}

.start, .stop, .reset {
    padding: 10px 20px 10px 20px;
    font-size: 1.5rem;
    font-weight: 600;
    color: black;
    cursor: pointer;
    background: transparent;
    justify-items: center;
}

@media (max-width: 767px) {
    .section {
        font-size: 1.75rem;
        margin-bottom: 40px;
    }
    .options{
        margin: 30px;
        flex-direction: column;
        width: 30vw;
    }
    .start, .stop, .reset {
       margin-bottom: 15px;
    }
}