* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-items: center;
  font-family: Arial, sans-serif;
  background: #eef2f7;
  color: #17202a;
}

main {
  width: min(720px, calc(100% - 24px));
  height: min(760px, calc(100vh - 24px));
  display: grid;
  grid-template-rows: auto 1fr auto;
  background: #fff;
  border: 1px solid #d8dde6;
}

header {
  padding: 18px 20px;
  border-bottom: 1px solid #d8dde6;
}

h1,
p {
  margin: 0;
}

p {
  color: #687385;
}

#messages {
  padding: 16px;
  overflow-y: auto;
  display: grid;
  align-content: start;
  gap: 10px;
}

.message {
  max-width: 78%;
  padding: 10px 12px;
  border: 1px solid #d8dde6;
  background: #f9fafb;
}

.message.me {
  margin-left: auto;
  background: #e6f4f1;
  border-color: #a4d9d0;
}

form {
  display: grid;
  grid-template-columns: 1fr 120px;
  gap: 10px;
  padding: 14px;
  border-top: 1px solid #d8dde6;
}

input,
button {
  min-height: 42px;
  border: 1px solid #d8dde6;
  padding: 8px 10px;
  font: inherit;
}

button {
  background: #0f766e;
  color: #fff;
  font-weight: 700;
  cursor: pointer;
}

@media (max-width: 520px) {
  form {
    grid-template-columns: 1fr;
  }
}