Down to the wire: Measure W sales tax, Measure X fire bond ahead by slimmest of margins

What is the determining factor if a new tax requires 50% plus one vote or two thirds approval to pass? I thought prop 13 settled all that years ago. That changed or am I missing something?
1978 California Proposition 13 - Wikipedia:
In addition to decreasing property taxes and changing the role of the state, Proposition 13 also contained language requiring a two-thirds (2/3) majority in both legislative houses for future increases of any state tax rates or amounts of revenue collected, including income tax rates and sales tax rates.