In 2011, the Company adopted the Equity Incentive Plan (2011 Plan) authorizing the granting of incentive stock options (ISOs) and non-statutory stock options (NSOs) to eligible participants for up to 12,987,255 shares of common stock. Under the 2011 Plan, incentive stock options and non-statutory stock options are to be granted at an exercise price that is no less than 100% of the fair value of the stock at the date of grant. Options generally vest over four years and are exercisable for up to 10 years after the date of grant. Incentive stock options granted to stockholders who own more than 10% of the outstanding stock of the Company at the time of grant must be issued at an exercise price no less than 110% of the fair value of the stock on the date of grant. The 2011 Plan has been replaced by the Company’s 2019 Plan as defined below with respect to future equity awards.

In connection with the Company’s initial public offering, the Company adopted the 2019 Equity Incentive Plan (the “2019 Plan”). The 2019 Plan allows the Company to grant stock options, stock appreciation rights, restricted stock, restricted stock units and performance awards to participants. Subject to the terms and conditions of the 2019 Plan, the initial number of shares authorized for grants under the 2019 Plan is 8,000,000. These available shares increase annually by an amount equal to the lesser of 8,000,000 shares, 5% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31, or the number of shares determined by the Company’s board of directors. On August 4, 2020, the Company’s board of directors approved an increase of shares available for grant under the 2019 Plan by 4,293,616 shares.

In connection with the Company’s initial public offering, the Company adopted the Employee Stock Purchase Plan (ESPP). The Employee Stock Purchase Plan permits employees to purchase shares of common stock during six-month offering periods at a purchase price equal to the lesser of (1) 85% of the fair market value of a share of common stock on the first business day of such offering period and (2) 85% of the fair market value of a share of common stock on the last business day of such offering period. The plan is considered compensatory and, as such, the purchase discount from market price purchased by employees will be recorded as compensation expense. The initial number of shares of common stock that could be issued under the employee stock purchase plan was 1,750,000 shares. These available shares increase by an amount equal to the lesser of 1,750,000 shares, 1% of the number of shares of common stock outstanding on the immediately preceding December 31, or the number of shares determined by the Company’s board of directors. On August 4, 2020, the Company’s board of directors approved an increase in the shares available for grant under the ESPP by 858,723 shares. The initial offering period ran from May 15, 2020 to November 14, 2020. There were no shares purchased by employees under the ESPP during the three months ended March 31, 2021 and 2020. The Company selected the Black-Scholes option-pricing model as the method for determining the estimated fair value for the Company’s 2019 ESPP. As of March 31, 2021, total unrecognized compensation costs related to the 2019 ESPP was $0.1 million which will be amortized over a weighted average period of 0.1 years.

Total stock-based compensation expense by function was as follows (in thousands):

	Three Months Ended March 31,
	2021		2020
Marketing	$	736	$	188
Operations and technology		4,696		1,478
Selling, general and administrative		5,487		1,744
Total	$	10,919	$	3,410

During the three months ended March 31, 2021, the Company capitalized $0.4 million of stock-based compensation expense to proprietary software. During the three months ended March 31, 2020, we did not capitalize any stock-based compensation expense.