style.css

* {
    box-sizing: border-box;
}

body {
    height: 100vh;
    margin: 0;
    overflow: hidden;
}
:root {
    --building-color1: #aa80ff;
    --building-color2: #66cc99;
    --building-color3: #cc6699;
    --building-color4: #538cc6;
    --window-color1: #bb99ff;
    --window-color2: #8cd9b3;
    --window-color3: #d98cb3;
    --window-color4: #8cb3d9;
}

.background-buildings,
.foreground-buildings {
    width: 100%;
    height: 100%;
    display: flex;
    align-items: flex-end;
    justify-content: space-evenly;
    position: absolute;
    top: 0;
}

.building-wrap {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.window-wrap {
    display: flex;
    align-items: center;
    justify-content: space-evenly;
}

.sky {
    background: radial-gradient(closest-corner circle at 15% 15%,
            #ffcf33,
            #ffcf33 20%,
            #ffff66 21%,
            #bbeeff 100%);
}

/* BACKGROUND BUILDINGS - "bb" stands for "background building" */
.bb1 {
    width: 10%;
    height: 70%;
}

.bb1a {
    width: 70%;
}

.bb1b {
    width: 80%;
}

.bb1c {
    width: 90%;
}

.bb1d {
    width: 100%;
    height: 70%;
    background: linear-gradient(var(--building-color1) 50%,
            var(--window-color1));
}

.bb1-window {
    height: 10%;
    background: linear-gradient(var(--building-color1),
            var(--window-color1));
}

.bb2 {
    width: 10%;
    height: 50%;
}

.bb2a {
    border-bottom: 5vh solid var(--building-color2);
    border-left: 5vw solid transparent;
    border-right: 5vw solid transparent;
}

.bb2b {
    width: 100%;
    height: 100%;
    background: repeating-linear-gradient(var(--building-color2),
            var(--building-color2) 6%,
            var(--window-color2) 6%,
            var(--window-color2) 9%);
}

.bb3 {
    width: 10%;
    height: 55%;
    background: repeating-linear-gradient(90deg,
            var(--building-color3),
            var(--building-color3),
            var(--window-color3) 15%);
}

.bb4 {
    width: 11%;
    height: 58%;
}

.bb4a {
    width: 3%;
    height: 10%;
    background-color: var(--building-color4);
}

.bb4b {
    width: 80%;
    height: 5%;
    background-color: var(--building-color4);
}

.bb4c {
    width: 100%;
    height: 85%;
    background-color: var(--building-color4);
}

.bb4-window {
    width: 18%;
    height: 90%;
    background-color: var(--window-color4);
}

/* FOREGROUND BUILDINGS - "fb" stands for "foreground building" */
.fb1 {
    width: 10%;
    height: 60%;
}

.fb1a {
    border-bottom: 7vh solid var(--building-color4);
    border-left: 2vw solid transparent;
    border-right: 2vw solid transparent;
}

.fb1b {
    width: 60%;
    height: 10%;
    background-color: var(--building-color4);
}

.fb1c {
    width: 100%;
    height: 80%;
    background: repeating-linear-gradient(90deg,
            var(--building-color4),
            var(--building-color4) 10%,
            transparent 10%,
            transparent 15%),
        repeating-linear-gradient(var(--building-color4),
            var(--building-color4) 10%,
            var(--window-color4) 10%,
            var(--window-color4) 90%);
}

.fb2 {
    width: 10%;
    height: 40%;
}

.fb2a {
    width: 100%;
    border-bottom: 10vh solid var(--building-color3);
    border-left: 1vw solid transparent;
    border-right: 1vw solid transparent;
}

.fb2b {
    width: 100%;
    height: 75%;
    background-color: var(--building-color3);
}

.fb2-window {
    width: 22%;
    height: 100%;
    background-color: var(--window-color3);
}

.fb3 {
    width: 10%;
    height: 35%;
}

.fb3a {
    width: 80%;
    height: 15%;
    background-color: var(--building-color1);
}

.fb3b {
    width: 100%;
    height: 35%;
    background-color: var(--building-color1);
}

.fb3-window {
    width: 25%;
    height: 80%;
    background-color: var(--window-color1);
}

.fb4 {
    width: 8%;
    height: 45%;
    position: relative;
    left: 10%;
}

.fb4a {
    border-top: 5vh solid transparent;
    border-left: 8vw solid var(--building-color1);
}

.fb4b {
    width: 100%;
    height: 89%;
    background-color: var(--building-color1);
    display: flex;
    flex-wrap: wrap;
}

.fb4-window {
    width: 30%;
    height: 10%;
    border-radius: 50%;
    background-color: var(--window-color1);
    margin: 10%;
}

.fb5 {
    width: 10%;
    height: 33%;
    position: relative;
    right: 10%;
    background: repeating-linear-gradient(var(--building-color2),
            var(--building-color2) 5%,
            transparent 5%,
            transparent 10%),
        repeating-linear-gradient(90deg,
            var(--building-color2),
            var(--building-color2) 12%,
            var(--window-color2) 12%,
            var(--window-color2) 44%);
}

.fb6 {
    width: 9%;
    height: 38%;
    background: repeating-linear-gradient(90deg,
            var(--building-color3),
            var(--building-color3) 10%,
            transparent 10%,
            transparent 30%),
        repeating-linear-gradient(var(--building-color3),
            var(--building-color3) 10%,
            var(--window-color3) 10%,
            var(--window-color3) 30%);
}

@media (max-width: 1000px) {
    :root {
        --building-color1: #000;
        --building-color2: #000;
        --building-color3: #000;
        --building-color4: #000;
        --window-color1: #777;
        --window-color2: #777;
        --window-color3: #777;
        --window-color4: #777;
    }
    .sky {
    background: radial-gradient(
        closest-corner circle at 15% 15%,
        #ccc,
        #ccc 20%,
        #445 21%,
        #223 100%
      );
  }
}