404.css

html,
body {
    height: 100%;
    width: 100%;
    margin: 0px;
    background: linear-gradient(90deg, rgba(47,54,64,1) 23%, rgba(24,27,32,1) 100%);
}

.moon {
    background: linear-gradient(90deg, rgba(208,208,208,1) 48%, rgba(145,145,145,1) 100%);
    position: absolute;
    top: -100px;
    left: -300px;
    width: 900px;
    height: 900px;
    content: '';
    border-radius: 100%;
    box-shadow: 0px 0px 30px -4px rgba(0,0,0,0.5);
}

.moon__crater {
    position: absolute;
    content: '';
    border-radius: 100%;
    background: linear-gradient(90deg, rgba(122,122,122,1) 38%, rgba(195,195,195,1) 100%);
    opacity: 0.6;
}

.moon__crater1 {
    top: 250px;
    left: 500px;
    width: 60px;
    height: 180px;
}

.moon__crater2 {
    top: 650px;
    left: 340px;
    width: 40px;
    height: 80px;
    transform: rotate(55deg);
}

.moon__crater3 {
    top: -20px;
    left: 40px;
    width: 65px;
    height: 120px;
    transform: rotate(250deg);
}

.star {
    background: grey;
    position: absolute;
    width: 5px;
    height: 5px;
    content: '';
    border-radius: 100%;
    transform: rotate(250deg);
    opacity: 0.4;
    animation-name: shimmer;
    animation-duration: 1.5s;
    animation-iteration-count: infinite;
    animation-direction: alternate;
}

@keyframes shimmer {
    from {opacity: 0;}
    to {opacity: 0.7;}
}

.star1 {
    top: 40%;
    left: 50%;
    animation-delay: 1s;
}

.star2 {
    top: 60%;
    left: 90%;
    animation-delay: 3s;
}

.star3 {
    top: 10%;
    left: 70%;
    animation-delay: 2s;
}

.star4 {
    top: 90%;
    left: 40%;
}

.star5 {
    top: 20%;
    left: 30%;
    animation-delay: 0.5s;
}

.error {
    position: absolute;
    left: 100px;
    top: 400px;
    transform: translateY(-60%);
    font-family: 'Righteous', cursive;
    color: #363e49;
}

.error__title {
    font-size: 10em;
}

.error__subtitle {
    font-size: 2em;
}

.error__description {
    opacity: 0.5;
}

.error__button {
    min-width: 7em;
    margin-top: 3em;
    margin-right: 0.5em;
    padding: 0.5em 2em;
    outline: none;
    border: 2px solid #2f3640;
    background-color: transparent;
    border-radius: 8em;
    color: #576375;
    cursor: pointer;
    transition-duration: 0.2s;
    font-size: 0.75em;
    font-family: 'Righteous', cursive;
}

.error__button:hover {
    color: #21252c;
}

.error__button--active {
    background-color: #e67e22;
    border: 2px solid #e67e22;
    color: white;
}

.error__button--active:hover {
    box-shadow: 0px 0px 8px 0px rgba(0,0,0,0.5);
    color: white;
}

.astronaut {
    position: absolute;
    width: 185px;
    height: 300px;
    left: 70%;
    top: 50%;
    transform: translate(-50%, -50%) rotate(20deg) scale(1.2);
}

.astronaut__head {
    background-color: white;
    position: absolute;
    top: 60px;
    left: 60px;
    width: 60px;
    height: 60px;
    content: '';
    border-radius: 2em;
}

.astronaut__head-visor-flare1 {
    background-color: #7f8fa6;
    position: absolute;
    top: 28px;
    left: 40px;
    width: 10px;
    height: 10px;
    content: '';
    border-radius: 2em;
    opacity: 0.5;
}

.astronaut__head-visor-flare2 {
    background-color: #718093;
    position: absolute;
    top: 40px;
    left: 38px;
    width: 5px;
    height: 5px;
    content: '';
    border-radius: 2em;
    opacity: 0.3;
}

.astronaut__backpack {
    background-color: #bfbfbf;
    position: absolute;
    top: 90px;
    left: 47px;
    width: 86px;
    height: 90px;
    content: '';
    border-radius: 8px;
}

.astronaut__body {
    background-color: #e6e6e6;
    position: absolute;
    top: 115px;
    left: 55px;
    width: 70px;
    height: 80px;
    content: '';
    border-radius: 8px;
}

.astronaut__body__chest {
    background-color: #d9d9d9;
    position: absolute;
    top: 140px;
    left: 68px;
    width: 45px;
    height: 25px;
    content: '';
    border-radius: 6px;
}

.astronaut__arm-left1 {
    background-color: #e6e6e6;
    position: absolute;
    top: 127px;
    left: 9px;
    width: 65px;
    height: 20px;
    content: '';
    border-radius: 8px;
    transform: rotate(-30deg);
}

.astronaut__arm-left2 {
    background-color: #e6e6e6;
    position: absolute;
    top: 102px;
    left: 7px;
    width: 20px;
    height: 45px;
    content: '';
    border-radius: 8px;
    transform: rotate(-12deg);
    border-top-left-radius: 8em;
    border-top-right-radius: 8em;
}

.astronaut__arm-right1 {
    background-color: #e6e6e6;
    position: absolute;
    top: 113px;
    left: 100px;
    width: 65px;
    height: 20px;
    content: '';
    border-radius: 8px;
    transform: rotate(-10deg);
}

.astronaut__arm-right2 {
    background-color: #e6e6e6;
    position: absolute;
    top: 78px;
    left: 141px;
    width: 20px;
    height: 45px;
    content: '';
    border-radius: 8px;
    transform: rotate(-10deg);
    border-top-left-radius: 8em;
    border-top-right-radius: 8em;
}

.astronaut__arm-thumb-left {
    background-color: #e6e6e6;
    position: absolute;
    top: 110px;
    left: 21px;
    width: 10px;
    height: 6px;
    content: '';
    border-radius: 8em;
    transform: rotate(-35deg);
}

.astronaut__arm-thumb-right {
    background-color: #e6e6e6;
    position: absolute;
    top: 90px;
    left: 133px;
    width: 10px;
    height: 6px;
    content: '';
    border-radius: 8em;
    transform: rotate(20deg);
}

.astronaut__wrist-left {
    background-color: #e67e22;
    position: absolute;
    top: 122px;
    left: 6.5px;
    width: 21px;
    height: 4px;
    content: '';
    border-radius: 8em;
    transform: rotate(-15deg);
}

.astronaut__wrist-right {
    background-color: #e67e22;
    position: absolute;
    top: 98px;
    left: 141px;
    width: 21px;
    height: 4px;
    content: '';
    border-radius: 8em;
    transform: rotate(-10deg);
}

.astronaut__leg-left {
    background-color: #e6e6e6;
    position: absolute;
    top: 188px;
    left: 50px;
    width: 23px;
    height: 75px;
    content: '';
    transform: rotate(10deg);
}

.astronaut__leg-right {
    background-color: #e6e6e6;
    position: absolute;
    top: 188px;
    left: 108px;
    width: 23px;
    height: 75px;
    content: '';
    transform: rotate(-10deg);
}

.astronaut__foot-left {
    background-color: white;
    position: absolute;
    top: 240px;
    left: 43px;
    width: 28px;
    height: 20px;
    content: '';
    transform: rotate(10deg);
    border-radius: 3px;
    border-top-left-radius: 8em;
    border-top-right-radius: 8em;
    border-bottom: 4px solid #e67e22;
}

.astronaut__foot-right {
    background-color: white;
    position: absolute;
    top: 240px;
    left: 111px;
    width: 28px;
    height: 20px;
    content: '';
    transform: rotate(-10deg);
    border-radius: 3px;
    border-top-left-radius: 8em;
    border-top-right-radius: 8em;
    border-bottom: 4px solid #e67e22;
}