Scrollable gradient chat bubble

Question

I want a white container with a chat bubble with a gradient that changes when scrolling with the gradient below, as shown in this example:

I tried making the .container part behind any chatBubble transparent so that the background of .root was visible.

.root {
  background-color: linear-gradient(red, yellow);
  width: 100vw;
  height: 100vh;
}

.container {
  width: 100%;
  height: 100vh;
  background-color: white
}

.chatBubble {
  background-color: transparent;
  border-radius: 4px;
  min-width: 50;
  padding: 10px;
}

<div class="root">
  <div class="container">
    <chatBubble>This is a chat bubble</chatBubble>
    <chatBubble>This is another chat bubble</chatBubble>
  </div>
</div>

Answer 1

This is what I've got so far, trying to mask it so I can have a white background to go with the gradient.

html,
body,
.container {
  height: 100%;
}

body {
  margin: 0;
  font-family: system-ui;
}

.container {
  display: flex;
  flex-flow: column nowrap;
  max-width: 60ch;
  margin: auto;
  padding: 1rem;
  background-color: white;
}

.container::before {
  content: '';
  position: fixed;
  inset: 0;
  background: linear-gradient(red, yellow);
}

.bubble {
  z-index: 1;
  min-width: 50px;
  width: fit-content;
  background-color: #eee;
  border-radius: 4px;
  padding: 0.5em;
  margin: 0.2em;
  text-wrap: balance;
}

.bubble.primary {
  color: white;
  background-color: transparent;
  background-blend-mode: multiply;
  align-self: end;
  text-align: end;
}

<div class="container">
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
</div>

Answer 2

You can "Place Shadow" from .bubble:

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

.container {
  --gap: 20px;
  --width: 800px;
  --background: #fff;
  display: flex;
  flex-direction: column;
  max-width: var(--width);
  margin: 16px auto;
  padding: 0 16px;
  overflow: hidden;
  gap: var(--gap);
  box-shadow: 0 0 0 100vw var(--background);
  font-family: sans-serif;
}

.container:before {
  content: '';
  inset: 0;
  position: fixed;
  z-index: -1;
  background: linear-gradient(purple, blue);
}

.bubble {
  max-width: 80%;
  background-color: lightgray;
  border-radius: 16px;
  padding: 8px 16px;
  box-shadow: 0 0 0 var(--gap) var(--background);
  position: relative;
}

.bubble::before,
.bubble::after {
  content: '';
  position: absolute;
  inset: calc(var(--gap) / -2) auto;
  background-color: var(--background);
  width: var(--width);
}

.bubble::before {
  right: 100%;
}

.bubble::after {
  left: 100%;
}

.bubble.primary {
  background-color: transparent;
  color: #fff;
  align-self: flex-end;
}

<div class="container">
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
  <div class="bubble">show weekend?</div>
  <div class="bubble primary">I'm down!</div>
  <div class="bubble">lets do this its been way to long since we were all together!</div>
  <div class="bubble primary ">Whos down for a pregame</div>
  <div class="bubble">YES! I got the day off! Say when and where?</div>
  <div class="bubble primary">Hows about Old Town at 4? we can get some grub and then head over to the venue</div>
  <div class="bubble">Yeah getting the band back together</div>
</div>