Slanted stripes on a page

I would like some full sized slanted stripes on the page; that's all.

This is what I did so far:

html, body {
    overflow-x: hidden;
    margin: 0;
    padding: 0;
}
body {
    display: flex;
    margin: 0;
    padding: 0;
}

.flag-strip {
    position: absolute;
    width: 100vw;
    height: 15px;
    left: 0;
    transform: rotate(-10deg);
    z-index: 1;
}

.flag-strip.red {
    background-color: #D90012;
    top: 9%;
}

.flag-strip.blue {
    background-color: #0033A0;
    top: 10.5%;
}

.flag-strip.orange {
    background-color: #F2A800;
    top: 12%;
}

@media (max-width: 878px) {
    .flag-strip.red {
        top: 11%;
    }

    .flag-strip.blue {
        top: 12.5%;
    }

    .flag-strip.orange {
        top: 14%;
    }
}

<div class="flag-strip red"></div>
<div class="flag-strip blue"></div>
<div class="flag-strip orange"></div>

But the user shouldn't have a horizontal scroll bar, and the stripes should be really full sized -- there shouldn't be any endings visible on the page.

How can I make it work like that?

Solution

You can do this entirely in CSS with linear-gradient as the background.

html, body {
    margin: 0;
    padding: 0;
    height: 100vh;
}
.flag-bg {
    height: 100%;
    
    --flag-a: 10deg;
    --flag-h: 30px;
    --flag-pos: 20%;
    --flag-color1: #D90012;
    --flag-color2: #0033A0;
    --flag-color3: #F2A800;
    --flag-antialias: 1px;
    background-image: linear-gradient(calc(180deg - var(--flag-a)),
      transparent        calc(var(--flag-pos) - var(--flag-antialias)),
      var(--flag-color1) calc(var(--flag-pos)),
      var(--flag-color1) calc(var(--flag-pos) + var(--flag-h) / 3 - var(--flag-antialias)),
      var(--flag-color2) calc(var(--flag-pos) + var(--flag-h) / 3),
      var(--flag-color2) calc(var(--flag-pos) + 2 * var(--flag-h) / 3 - var(--flag-antialias)),
      var(--flag-color3) calc(var(--flag-pos) + 2 * var(--flag-h) / 3),
      var(--flag-color3) calc(var(--flag-pos) + var(--flag-h) - var(--flag-antialias)),
      transparent        calc(var(--flag-pos) + var(--flag-h))
    );
    background-repeat: no-repeat;
}

<div class="flag-bg"></div>