style.css

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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    height: 100vh;
    overflow-x: hidden;
}
#message {
    position: absolute;
    width: 100%;
    height: 100vh;
    z-index: 100;
    display: flex;
    align-items: center;
    justify-content: space-evenly;
    flex-direction: column;
    background-image: linear-gradient(0deg,#cf0011 40%,#ff8b00 100%);
    /* opacity: 0; */
    color: white;
}
#message p, #message h2 {
    text-align: center;
    line-height: 1.5;
}
#message h2 {
    color: darkblue;
    font-size: 2rem;
    text-transform: uppercase;
    text-shadow: darkblue 1px 1px;
}
#message p {
    font-size: 1.5rem;
}
#start {
    width: 20%;
    height: 7%;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    font-weight: 700;
    font-size: 1.4rem;
    font-family:system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    text-transform: uppercase;
    transition: all 0.2s linear;
}
#start:hover {
    letter-spacing: 2px;
}
.score-box {
    position: absolute;
    top: 0;
    width: 75%;
    max-width: 400px;
    height: 10vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #0081CF;
    border-bottom-left-radius: 50px;
    z-index: 105;
}
#score, .rem {
    height: 100%;
    width: 50%;
    position: relative;
}
.rem {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    border-left: 4px solid black;
}
#rem-bullet {
    border-bottom: 2px solid black;
}
.rem div {
    height: 100%;
    width: 100%;
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
}
.score-box p {
    width: 100%;
    height: 50%;
    text-align: center;
    font-size: 1.3rem;
    color: whitesmoke;
}

#score p {
    font-size: 1.6rem;
    font-family: fantasy;
    letter-spacing: 1px;
}
.outer {
    position: relative;
    width: 100%;
    /* max-width: 400px; */
    height: 100vh;
    /* max-height: 600px; */
    background-color: white;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
    border-radius: 15px;
}
.outer::before {
    content: '';
    position: absolute;
    width: 500%;
    height: 500%;
    background:  conic-gradient(transparent,transparent,transparent,blue);
    animation: animate 4s linear  infinite  ;
}
.outer::after {
    content: '';
    position: absolute;
    width: 500%;
    height: 500%;
    background:  conic-gradient(transparent,transparent,transparent,red);
    animation: animate 4s linear -2s infinite  ;
}

@keyframes animate {
    0% {

    }
    100% {
        transform: rotate(360deg);
    }
}

.board {
    position: absolute;
    inset: 5px;
    /* background-color: #050505; */
    background-image: url(./image/bg3.jpg);
    background-position: center;
    background-size: cover;
    z-index: 2;
    border-radius: 10px;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
}

.rocket {
    width: 35px;
    height: 50px;
    position: absolute;
    bottom: 0;
    left: 50%;
    background-image: url(./image/rocket.png);
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center;
    /* outline: 2px red solid; */
}
.alien {
    position: absolute;
    width: 70px;
    height: 30px;
    top: 0;
    left: 0;
    background-image: url(./image/alien.png);
    background-position: center;
    background-size: contain;
    background-repeat: no-repeat;
    /* outline: 2px red solid; */
    z-index: 10;
}

.bullets {
    width: 15px;
    height: 35px;
    position: absolute;
    bottom: 50px;
    left: -50%;
    background-image: url(./image/bullet.png);
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center;
    /* outline: 2px red solid; */
}
.buttons {
    position: absolute;
    bottom: 0;
    display: none;
    justify-content: space-around;
    align-items: center;
    height: 10vh;
    width: 100%;
}
.buttons button {
    position: absolute;
    width: 20%;
    height: 7vh;
    min-height: 30px;
    border: none;
    border-radius: 10px;
    background-color: #34495E;
}
#fire {
    left: 10%;
    width: 25%;
    height: 9vh;
    background-image: url(./image/bullet.png);
    background-position: center;
    background-size: contain;
    background-repeat: no-repeat;
}
#right {
    left: 75%;
    background-image: url(./image/icons8-right-64.png);
    background-position: center;
    background-repeat: no-repeat;
    background-size: contain;
}
#left {
    left: 50%;
    background-image: url(./image/icons8-left-64.png);
    background-position: center;
    background-repeat: no-repeat;
    background-size: contain;
}


@media (max-width: 550px) {
    html {
        font-size: 9px;
    }
    body{
        justify-content: start;
    }
    .score-box {
        position: relative;
        width: 100%;
        max-width: 550px;
    }
    .outer {
        height: 70vh;
    }
    .buttons {
        display: flex;
    }

}