ar-design/dist/assets/css/components/form/input/phone/styles.css

AR Design is a (react | nextjs) ui library.

.ar-input-phone-wrapper {
  display: flex;
  flex-direction: row;

  > .ar-select-wrapper {
    flex: 0 0 20%;

    > .ar-select {
      > .ar-input-wrapper {
        > .ar-input {
          > .input {
            > input {
              border-right: none;
              border-radius: 0;
              border-top-left-radius: var(--border-radius-sm);
              border-bottom-left-radius: var(--border-radius-sm);
            }
          }
        }
      }
    }
  }

  > .ar-input-wrapper {
    flex: 1;

    > .ar-input {
      > .input {
        > input {
          border-radius: 0;
          border-top-right-radius: var(--border-radius-sm);
          border-bottom-right-radius: var(--border-radius-sm);
        }
      }
    }
  }

  /* @media (max-width: 600px) {
    flex-direction: column;

    .ar-select-wrapper,
    .ar-input-wrapper {
      flex: 1 1 100%;

      .ar-input .input input {
        border-radius: var(--border-radius-sm);
      }
    }
  } */
}