.flex-container
  .block.block-1 this_text_will_not_wrap
  .block.block-2 this_text_will_not_wrap

.flex-container {
  display: flex;
  justify-content: space-between;
}

.block {
  flex-grow: 0;
  flex-shrink: 1;
  height: 100px;
  background-color: pink;
  border: 1px solid black;
}

.block-1 {
  flex-basis: 600px;
}

.block-2 {
  flex-basis: 300px;
}