Short answer will be: there are no 'Junior web-designer' positions in Zürich as permanent job. Most companies outsource tasks that require junior competencies to other countries with less expensive workforce, or to freelancers.
Even if there is a position for junior, it is typically filled with German-speaking students, interns or apprentices, often as a part-time (40-60%) job.
When it comes to a salary, then my experience says it might be 45-65 kCHF gross per year. Working conditions and benefits may vary.